part I

found distinctly in my breast, that I had imbibed a part of it; nor was I free of an asthmatic sensation till I had been some months in Italy." Bruce's Travels. Vol. IV. p. 557.

It is difficult to account for the narrow track of this pestilential wind, which is said not to exceed twenty yards, and for its small elevation of twelve feet. A whirlwind will pass forwards, and throw down an avenue of trees by its quick revolution as it passes, but nothing like a whirling is described as happening in these narrow streams of air, and whirlwinds ascend to greater heights. There seems but one known manner in which this channel of air could be effected, and that is by electricity.

The volcanic origin of these winds is mentioned in the note on Chunda in Vol. II. of this work; it must here be added, that Professor Vairo at Naples found, that during the eruption of Vesuvius perpendicular iron bars were electric; and others have observed suffocating damps to attend these eruptions. Ferber's Travels in Italy, p. 133. And lastly, that a current of air attends the passage of electric matter, as is seen in presenting an electrized point to the flame of a candle. In Mr. Bruce's account of this simoom, it was in its course over a quite dry desert of sand, (and which was in consequence unable to conduct an electric stream into the earth beneath it,) to some moist rocks at but a few miles distance; and thence would appear to be a stream of electricity from a volcano attended with noxious air; and as the bodies of Mr. Bruce and his attendants were insulated on the sand, they would not be sensible of their increased electricity, as it passed over them; to which it may be added, that a sulphurous or suffocating sensation is said to accompany flames of lightning, and even strong sparks of artificial electricity. In the above account of the simoom, a great redness in the air is said to be a certain sign of its approach, which may be occasioned by the eruption of flame from a distant volcano in these extensive and impenetrable deserts of sand. See Note on l. 294 of this Canto.]

You seize TORNADO by his locks of mist, Burst his dense clouds, his wheeling spires untwist; Wide o'er the West when borne on headlong gales, Dark as meridian night, the Monster sails, 75 Howls high in air, and shakes his curled brow, Lashing with serpent-train the waves below, Whirls his black arm, the forked lightning flings, And showers a deluge from his demon-wings.

[_Tornado's_. l. 71. See additional notes, No. XXXIII.]

2. "SYLPHS! with light shafts YOU pierce the drowsy FOG, 80 That lingering slumbers on the sedge-wove bog, With webbed feet o'er midnight meadows creeps, Or flings his hairy limbs on stagnant deeps. YOU meet CONTAGION issuing from afar, And dash the baleful conqueror from his car; 85 When, Guest of DEATH! from charnel vaults he steals, And bathes in human gore his armed wheels.

[_On stagnant deeps_. l. 82. All contagious miasmata originate either from animal bodies, as those of the small pox, or from putrid morasses; these latter produce agues in the colder climates, and malignant fevers in the warmer ones. The volcanic vapours which cause epidemic coughs, are to be ranked amongst poisons, rather than amongst the miasmata, which produce contagious diseases.]

"Thus when the PLAGUE, upborne on Belgian air, Look'd through the mist and shook his clotted hair, O'er shrinking nations steer'd malignant clouds, 90 And rain'd destruction on the gasping crouds. The beauteous AEGLE felt the venom'd dart, Slow roll'd her eye, and feebly throbb'd her heart; Each fervid sigh seem'd shorter than the last, And starting Friendship shunn'd her, as she pass'd. 95 --With weak unsteady step the fainting Maid Seeks the cold garden's solitary shade, Sinks on the pillowy moss her drooping head, And prints with lifeless limbs her leafy bed. --On wings of Love her plighted Swain pursues, 100 Shades her from winds, and shelters her from dews, Extends on tapering poles the canvas roof, Spreads o'er the straw-wove matt the flaxen woof, Sweet buds and blossoms on her bolster strows, And binds his kerchief round her aching brows; 105 Sooths with soft kiss, with tender accents charms, And clasps the bright Infection in his arms.-- With pale and languid smiles the grateful Fair Applauds his virtues, and rewards his care; Mourns with wet cheek her fair companions fled 110 On timorous step, or number'd with the dead; Calls to its bosom all its scatter'd rays, And pours on THYRSIS the collected blaze; Braves the chill night, caressing and caress'd, And folds her Hero-lover to her breast.-- 115 Less bold, LEANDER at the dusky hour Eyed, as he swam, the far love-lighted tower; Breasted with struggling arms the tossing wave, And sunk benighted in the watery grave. Less bold, TOBIAS claim'd the nuptial bed, 120 Where seven fond Lovers by a Fiend had bled; And drove, instructed by his Angel-Guide, The enamour'd Demon from the fatal bride.-- --SYLPHS! while your winnowing pinions fan'd the air, And shed gay visions o'er the sleeping pair; 125 LOVE round their couch effused his rosy breath, And with his keener arrows conquer'd DEATH.

[_The beauteous Aegle_. l. 91. When the plague raged in Holland in 1636, a young girl was seized with it, had three carbuncles, and was removed to a garden, where her lover, who was betrothed to her, attended her as a nurse, and slept with her as his wife. He remained uninfected, and she recovered, and was married to him. The story is related by Vinc. Fabricius in the Misc. Cur. Ann. II. Obs. 188.]

IV. 1. "You charm'd, indulgent SYLPHS! their learned toil, And crown'd with fame your TORRICELL, and BOYLE; Taught with sweet smiles, responsive to their prayer, 130 The spring and pressure of the viewless air. --How up exhausted tubes bright currents flow Of liquid silver from the lake below, Weigh the long column of the incumbent skies, And with the changeful moment fall and rise. 135 --How, as in brazen pumps the pistons move, The membrane-valve sustains the weight above; Stroke follows stroke, the gelid vapour falls, And misty dew-drops dim the crystal walls; Rare and more rare expands the fluid thin, 140 And Silence dwells with Vacancy within.-- So in the mighty Void with grim delight Primeval Silence reign'd with ancient Night.

[_Torricell and Boyle_. l. 128. The pressure of the atmosphere was discovered by Torricelli, a disciple of Galileo, who had previously found that the air had weight. Dr. Hook and M. Du Hamel ascribe the invention of the air-pump to Mr. Boyle, who however confesses he had some hints concerning its construction from De Guerick. The vacancy at the summit of the barometer is termed the Torricellian vacuum, and the exhausted receiver of an air pump the Boylean vacuum, in honour of these two philosophers.

The mist and descending dew which appear at first exhausting the receiver of an air-pump, are explained in the Phil. Trans. Vol. LXXVIII. from the cold produced by the expansion of air. For a thermometer placed in the receiver sinks some degrees, and in a very little time, as soon as a sufficient quantity of heat can be acquired from the surrounding bodies, the dew becomes again taken up. See additional notes, No. VII. Mr. Saussure observed on placing his hygrometer in a receiver of an air- pump, that though on beginning to exhaust it the air became misty, and parted with its moisture, yet the hair of his hygrometer contracted, and the instrument pointed to greater dryness. This unexpected occurrence is explained by M. Monge (Annales de Chymie, Tom. V.) to depend on the want of the usual pressure of the atmosphere to force the aqueous particles into the pores of the hair; and M. Saussure supposes, that his vesicular vapour requires more time to be redissolved, than is necessary to dry the hair of his thermometer. Essais sur l'Hygrom. p. 226. but I suspect there is a less hypothetical way of understanding it; when a colder body is brought into warm and moist air, (as a bottle of spring-water for instance,) a steam is quickly collected on its surface; the contrary occurs when a warmer body is brought into cold and damp air, it continues free from dew so long as it continues warm; for it warms the atmosphere around it, and renders it capable of receiving instead of parting with moisture. The moment the air becomes rarefied in the receiver of the air-pump it becomes colder, as appears by the thermometer, and deposits its vapour; but the hair of Mr. Saussure's hygrometer is now warmer than the air in which it is immersed, and in consequence becomes dryer than before, by warming the air which immediately surrounds it, a part of its moisture evaporating along with its heat.]

2. "SYLPHS! your soft voices, whispering from the skies, Bade from low earth the bold MONGULFIER rise; 145 Outstretch'd his buoyant ball with airy spring, And bore the Sage on levity of wing;-- Where were ye, SYLPHS! when on the ethereal main Young ROSIERE launch'd, and call'd your aid in vain? Fair mounts the light balloon, by Zephyr driven, 150 Parts the thin clouds, and sails along the heaven; Higher and yet higher the expanding bubble flies, Lights with quick flash, and bursts amid the skies.-- Headlong He rushes through the affrighted air With limbs distorted, and dishevel'd hair, 155 Whirls round and round, the flying croud alarms, And DEATH receives him in his sable arms!-- So erst with melting wax and loosen'd strings Sunk hapless ICARUS on unfaithful wings; His scatter'd plumage danced upon the wave, 160 And sorrowing Mermaids deck'd his watery grave; O'er his pale corse their pearly sea-flowers shed, And strew'd with crimson moss his marble bed; Struck in their coral towers the pausing bell, And wide in ocean toll'd his echoing knell.

[_Young Rosiere launch'd_. l. 148. M. Pilatre du Rosiere with a M. Romain rose in a balloon from Boulogne in June 1785, and after having been about a mile high for about half an hour the balloon took fire, and the two adventurers were dashed to pieces on their fall to the ground. Mr. Rosiere was a philosopher of great talents and activity, joined with such urbanity and elegance of manners, as conciliated the affections of his acquaintance and rendered his misfortune universally lamented. Annual Register for 1784 and 1785, p. 329.]

[_And wide in ocean_. l. 164. Denser bodies propagate vibration or sound better than rarer ones; if two stones be struck together under the water, they may be heard a mile or two by any one whose head is immersed at that distance, according to an experiment of Dr. Franklin. If the ear be applied to one end of a long beam of timber, the stroke of a pin at the other end becomes sensible; if a poker be suspended in the middle of a garter, each end of which is pressed against the ear, the least percussions on the poker give great sounds. And I am informed by laying the ear on the ground the tread of a horse may be discerned at a great distance in the night. The organs of hearing belonging to fish are for this reason much less complicated than of quadrupeds, as the fluid they are immersed in so much better conveys its vibrations. And it is probable that some shell-fish which have twisted shells like the cochlea and semicircular canals of the ears of men and quadrupeds may have no appropriated organ for perceiving the vibrations of the element they live in, but may by their spiral form be in a manner all ear.]

165 V. "SYLPHS! YOU, retiring to sequester'd bowers, Where oft your PRIESTLEY woos your airy powers, On noiseless step or quivering pinion glide, As sits the Sage with Science by his side; To his charm'd eye in gay undress appear, 170 Or pour your secrets on his raptured ear. How nitrous Gas from iron ingots driven Drinks with red lips the purest breath of heaven; How, while Conferva from its tender hair Gives in bright bubbles empyrean air; 175 The crystal floods phlogistic ores calcine, And the pure ETHER marries with the MINE.

[_Where oft your Priestley_. l. 166. The fame of Dr. Priestley is known in every part of the earth where science has penetrated. His various discoveries respecting the analysis of the atmosphere, and the production of variety of new airs or gasses, can only be clearly understood by reading his Experiments on Airs, (3 vols. octavo, Johnson, London.) the following are amongst his many discoveries. 1. The discovery of nitrous and dephlogisticated airs. 2. The exhibition of the acids and alkalies in the form of air. 3. Ascertaining the purity of respirable air by nitrous air. 4. The restoration of vitiated air by vegetation. 5. The influence of light to enable vegetables to yield pure air. 6. The conversion by means of light of animal and vegetable substances, that would otherwise become putrid and offensive, into nourishment of vegetables. 7. The use of respiration by the blood parting with phlogiston, and imbibing dephlogisticated air.

The experiments here alluded to are, 1. Concerning the production of nitrous gas from dissolving iron and many other metals in nitrous acid, which though first discovered by Dr. Hales (Static. Ess. Vol. I. p. 224) was fully investigated, and applied to the important purpose of distinguishing the purity of atmospheric air by Dr. Priestley. When about two measures of common air and one of nitrous gas are mixed together a red effervescence takes place, and the two airs occupy about one fourth less space than was previously occupied by the common air alone.

2. Concerning the green substance which grows at the bottom of reservoirs of water, which Dr. Priestley discovered to yield much pure air when the sun shone on it. His method of collecting this air is by placing over the green substance, which he believes to be a vegetable of the genus conferva, an inverted bell-glass previously filled with water, which subsides as the air arises; it has since been found that all vegetables give up pure air from their leaves, when the sun shines upon them, but not in the night, which may be owing to the sleep of the plant.

3. The third refers to the great quantity of pure air contained in the calces of metals. The calces were long known to weigh much more than the metallic bodies before calcination, insomuch that 100 pounds of lead will produce 112 pounds of minium; the ore of manganese, which is always found near the surface of the earth, is replete with pure air, which is now used for the purpose of bleaching. Other metals when exposed to the atmosphere attract the pure air from it, and become calces by its combination, as zinc, lead, iron; and increase in weight in proportion to the air, which they imbibe.]

"So in Sicilia's ever-blooming shade When playful PROSERPINE from CERES stray'd, Led with unwary step her virgin trains 180 O'er Etna's steeps, and Enna's golden plains; Pluck'd with fair hand the silver-blossom'd bower, And purpled mead,--herself a fairer flower; Sudden, unseen amid the twilight glade, Rush'd gloomy DIS, and seized the trembling maid.-- 185 Her starting damsels sprung from mossy seats, Dropp'd from their gauzy laps the gather'd sweets, Clung round the struggling Nymph, with piercing cries, Pursued the chariot, and invoked the skies;-- Pleased as he grasps her in his iron arms, 190 Frights with soft sighs, with tender words alarms, The wheels descending roll'd in smoky rings, Infernal Cupids flapp'd their demon wings; Earth with deep yawn received the Fair, amaz'd, And far in Night celestial Beauty blaz'd.

[_When playful Proserpine_. l. 178. The fable of Proserpine's being seized by Pluto as she was gathering flowers, is explained by Lord Bacon to signify the combination or marriage of etherial spirit with earthly materials. Bacon's Works, Vol. V. p. 470. edit. 4to. Lond. 1778. This allusion is still more curiously exact, from the late discovery of pure air being given up from vegetables, and that then in its unmixed state it more readily combines with metallic or inflammable bodies. From these fables which were probably taken from antient hieroglyphics there is frequently reason to believe that the Egyptians possessed much chemical knowledge, which for want of alphabetical writing perished with their philosophers.]

195 VI. "Led by the Sage, Lo! Britain's sons shall guide Huge SEA-BALLOONS beneath the tossing tide; The diving castles, roof'd with spheric glass, Ribb'd with strong oak, and barr'd with bolts of brass, Buoy'd with pure air shall endless tracks pursue, 200 And PRIESTLEY'S hand the vital flood renew.-- Then shall BRITANNIA rule the wealthy realms, Which Ocean's wide insatiate wave o'erwhelms; Confine in netted bowers his scaly flocks, Part his blue plains, and people all his rocks. 205 Deep, in warm waves beneath the Line that roll, Beneath the shadowy ice-isles of the Pole, Onward, through bright meandering vales, afar, Obedient Sharks shall trail her sceptred car, With harness'd necks the pearly flood disturb, 210 Stretch the silk rein, and champ the silver curb; Pleased round her triumph wondering Tritons play, And Seamaids hail her on the watery way. --Oft shall she weep beneath the crystal waves O'er shipwreck'd lovers weltering in their graves; 215 Mingling in death the Brave and Good behold With slaves to glory, and with slaves to gold; Shrin'd in the deep shall DAY and SPALDING mourn, Each in his treacherous bell, sepulchral urn!-- Oft o'er thy lovely daughters, hapless PIERCE! 220 Her sighs shall breathe, her sorrows dew their hearse.-- With brow upturn'd to Heaven, "WE WILL NOT PART!" He cried, and clasp'd them to his aching heart,-- --Dash'd in dread conflict on the rocky grounds, Crash the mock'd masts, the staggering wreck rebounds; 225 Through gaping seams the rushing deluge swims, Chills their pale bosoms, bathes their shuddering limbs, Climbs their white shoulders, buoys their streaming hair, And the last sea-shriek bellows in the air.-- Each with loud sobs her tender sire caress'd, 230 And gasping strain'd him closer to her breast!-- --Stretch'd on one bier they sleep beneath the brine, And their white bones with ivory arms intwine!

[_Led by the Sage_. l. 195. Dr. Priestley's discovery of the production of pure air from such variety of substances will probably soon be applied to the improvement of the diving bell, as the substances which contain vital air in immense quantities are of little value as manganese and minium. See additional notes, No. XXXIII. In every hundred weight of minium there is combined about twelve pounds of pure air, now as sixty pounds of water are about a cubic foot, and as air is eight hundred times lighter than water, five hundred weight of minium will produce eight hundred cubic feet of air or about six thousand gallons. Now, as this is at least thrice as pure as atmospheric air, a gallon of it may be supposed to serve for three minutes respiration for one man. At present the air can not be set at liberty from minium by vitriolic acid without the application of some heat, this is however very likely soon to be discovered, and will then enable adventurers to journey beneath the ocean in large inverted ships or diving balloons.

Mr. Boyle relates, that Cornelius Drebelle contrived not only a vessel to be rowed under water, but also a liquor to be caried in that vessel, which would supply the want of fresh air. The vessel was made by order of James I. and carried twelve rowers besides passengers. It was tried in the river Thames, and one of the persons who was in that submarine voyage told the particulars of the experiments to a person who related them to Mr. Boyle. Annual Register for 1774, p. 248.]

[_Day and Spalding mourn_. l. 217. Mr. Day perished in a diving bell, or diving boat, of his own construction at Plymouth in June 1774, in which he was to have continued for a wager twelve hours one hundred feet deep in water, and probably perished from his not possessing all the hydrostatic knowledge that was necessary. See note on Ulva, Vol. II. of this work. See Annual Register for 1774. p. 245.

Mr. Spalding was professionally ingenious in the art of constructing and managing the diving bell, and had practised the business many years with success. He went down accompanied by one of his young men twice to view the wreck of the Imperial East-Indiaman at the Kish bank in Ireland. On descending the third time in June, 1783, they remained about an hour under water, and had two barrels of air sent down to them, but on the signals from below not being again repeated, after a certain time, they were drawn up by their assistants and both found dead in the bell. Annual Register for 1783, p. 206. These two unhappy events may for a time check the ardor of adventurers in traversing the bottom of the ocean, but it is probable in another half century it may be safer to travel under the ocean than over it, since Dr. Priestley's discovery of procuring pure air in such great abundance from the calces of metals.]

[_Hapless Pierce!_ l, 219. The Haslewell East-Indiaman, outward bound, was wrecked off Seacomb in the isle of Purbec on the 6th of January, 1786; when Capt. Pierce, the commander, with two young ladies, his daughters, and the greatest part of the crew and passengers perished in the sea. Some of the officers and about seventy seamen escaped with great difficulty on the rocks, but Capt. Pierce finding it was impossible to save the lives of the young ladies refused to quit the ship, and perished with them.]

"VII. SYLPHS OF NICE EAR! with beating wings you guide The fine vibrations of the aerial tide; 235 Join in sweet cadences the measured words, Or stretch and modulate the trembling cords. You strung to melody the Grecian lyre, Breathed the rapt song, and fan'd the thought of fire, Or brought in combinations, deep and clear, 240 Immortal harmony to HANDEL'S ear.-- YOU with soft breath attune the vernal gale, When breezy evening broods the listening vale; Or wake the loud tumultuous sounds, that dwell In Echo's many-toned diurnal shell. 245 YOU melt in dulcet chords, when Zephyr rings The Eolian Harp, and mingle all its strings; Or trill in air the soft symphonious chime, When rapt CECILIA lifts her eye sublime, Swell, as she breathes, her bosoms rising snow, 250 O'er her white teeth in tuneful accents slow, Through her fair lips on whispering pinions move, And form the tender sighs, that kindle love!

"So playful LOVE on Ida's flowery sides With ribbon-rein the indignant Lion guides; 255 Pleased on his brinded back the lyre he rings, And shakes delirious rapture from the strings; Slow as the pausing Monarch stalks along, Sheaths his retractile claws, and drinks the song; Soft Nymphs on timid step the triumph view, 260 And listening Fawns with beating hoofs pursue; With pointed ears the alarmed forest starts, And Love and Music soften savage hearts.

[_Indignant lion guides_. l. 254. Described from an antient gem, expressive of the combined power of love and music, in the Museum Florent.]

VIII. "SYLPHS! YOUR bold hosts, when Heaven with justice dread Calls the red tempest round the guilty head, 265 Fierce at his nod assume vindictive forms, And launch from airy cars the vollied storms.-- From Ashur's vales when proud SENACHERIB trod, Pour'd his swoln heart, defied the living GOD, Urged with incessant shouts his glittering powers; 270 And JUDAH shook through all her massy towers; Round her sad altars press'd the prostrate crowd, Hosts beat their breasts, and suppliant chieftains bow'd; Loud shrieks of matrons thrill'd the troubled air, And trembling virgins rent their scatter'd hair; 275 High in the midst the kneeling King adored, Spread the blaspheming scroll before the Lord, Raised his pale hands, and breathed his pausing sighs, And fixed on Heaven his dim imploring eyes,-- "Oh! MIGHTY GOD! amidst thy Seraph-throng 280 "Who sit'st sublime, the Judge of Right and Wrong; "Thine the wide earth, bright sun, and starry zone, "That twinkling journey round thy golden throne; "Thine is the crystal source of life and light, "And thine the realms of Death's eternal night. 285 "Oh, bend thine ear, thy gracious eye incline, "Lo! Ashur's King blasphemes thy holy shrine, "Insults our offerings, and derides our vows,--- "Oh! strike the diadem from his impious brows, "Tear from his murderous hand the bloody rod, 290 "And teach the trembling nations, "THOU ART GOD!"-- --SYLPHS! in what dread array with pennons broad Onward ye floated o'er the ethereal road, Call'd each dank steam the reeking marsh exhales, Contagious vapours, and volcanic gales, 295 Gave the soft South with poisonous breath to blow, And rolled the dreadful whirlwind on the foe!-- Hark! o'er the camp the venom'd tempest sings, Man falls on Man, on buckler buckler rings; Groan answers groan, to anguish anguish yields, 300 And DEATH'S loud accents shake the tented fields! --High rears the Fiend his grinning jaws, and wide Spans the pale nations with colossal stride, Waves his broad falchion with uplifted hand, And his vast shadow darkens all the land.

[_Volcanic gales_. l. 294. The pestilential winds of the east are described by various authors under various denominations; as harmattan, samiel, samium, syrocca, kamsin, seravansum. M. de Beauchamp describes a remarkable south wind in the deserts about Bagdad, called seravansum, or poison-wind; it burns the face, impedes respiration, strips the trees of their leaves, and is said to pass on in a streight line, and often kills people in six hours. P. Cotte sur la Meteorol. Analytical Review for February, 1790. M. Volney says, the hot wind or ramsin seems to blow at the season when the sands of the deserts are the hottest; the air is then filled with an extreamly subtle dust. Vol. I. p. 61. These winds blow in all directions from the deserts; in Egypt the most violent proceed from the S.S.W. at Mecca from the E. at Surat from the N. at Bassora from the N.W. at Bagdad from the W. and in Syria from the S.E.

On the south of Syria, he adds, where the Jordan flows is a country of volcanos; and it is observed that the earthquakes in Syria happen after their rainy season, which is also conformable to a similar observation made by Dr. Shaw in Barbary. Travels in Egypt, Vol. I. p. 303.

These winds seem all to be of volcanic origin, as before mentioned, with this difference, that the Simoom is attended with a stream of electric matter; they seem to be in consequence of earthquakes caused by the monsoon floods, which fall on volcanic fires in Syria, at the same time that they inundate the Nile.]

305 IX. 1. "Ethereal cohorts! Essences of Air! Make the green children of the Spring your care! Oh, SYLPHS! disclose in this inquiring age One GOLDEN SECRET to some favour'd sage; Grant the charm'd talisman, the chain, that binds, 310 Or guides the changeful pinions of the winds! --No more shall hoary Boreas, issuing forth With Eurus, lead the tempests of the North; Rime the pale Dawn, or veil'd in flaky showers Chill the sweet bosoms of the smiling Hours. 315 By whispering Auster waked shall Zephyr rise, Meet with soft kiss, and mingle in the skies, Fan the gay floret, bend the yellow ear, And rock the uncurtain'd cradle of the year; Autumn and Spring in lively union blend, 320 And from the skies the Golden Age descend.

[_One golden secret_. l. 308. The suddenness of the change of the wind from N.E. to S.W. seems to shew that it depends on some minute chemical cause; which if it was discovered might probably, like other chemical causes, be governed by human agency; such as blowing up rocks by gunpowder, or extracting the lightening from the clouds. If this could be accomplished, it would be the most happy discovery that ever has happened to these northern latitudes, since in this country the N.E. winds bring frost, and the S.W. ones are attended with warmth and moisture; if the inferior currents of air could be kept perpetually from the S.W. supplied by new productions of air at the line, or by superior currents flowing in a contrary direction, the vegetation of this country would be doubled; as in the moist vallies of Africa, which know no frost; the number of its inhabitants would be increased, and their lives prolonged; as great abundance of the aged and infirm of mankind, as well as many birds and animals, are destroyed by severe continued frosts in this climate.]

2. "Castled on ice, beneath the circling Bear, A vast CAMELION spits and swallows air; O'er twelve degrees his ribs gigantic bend, And many a league his leathern jaws extend; 325 Half-fish, beneath, his scaly volutes spread, And vegetable plumage crests his head; Huge fields of air his wrinkled skin receives, From panting gills, wide lungs, and waving leaves; Then with dread throes subsides his bloated form, 330 His shriek the thunder, and his sigh the storm. Oft high in heaven the hissing Demon wins His towering course, upborne on winnowing fins; Steers with expanded eye and gaping mouth, His mass enormous to the affrighted South; 335 Spreads o'er the shuddering Line his shadowy limbs, And Frost and Famine follow as he swims.-- SYLPHS! round his cloud-built couch your bands array, And mould the Monster to your gentle sway; Charm with soft tones, with tender touches check, 340 Bend to your golden yoke his willing neck, With silver curb his yielding teeth restrain, And give to KIRWAN'S hand the silken rein. --Pleased shall the Sage, the dragon-wings between, Bend o'er discordant climes his eye serene, 345 With Lapland breezes cool Arabian vales, And call to Hindostan antarctic gales, Adorn with wreathed ears Kampschatca's brows, And scatter roses on Zealandic snows, Earth's wondering Zones the genial seasons share, 350 And nations hail him "MONARCH OF THE AIR."

[_A vast Camelion_. l. 322. See additional notes, No. XXXIII. on the destruction and reproduction of the atmosphere.]

[_To Kirwan's hand_. l. 342. Mr. Kirwan has published a valuable treatise on the temperature of climates, as a step towards investigating the theory of the winds; and has since written some ingenious papers on this subject in the Transactions of the Royal Irish Society.]

X. 1. "SYLPHS! as you hover on ethereal wing, Brood the green children of parturient Spring!-- Where in their bursting cells my Embryons rest, I charge you guard the vegetable nest; 355 Count with nice eye the myriad SEEDS, that swell Each vaulted womb of husk, or pod, or shell; Feed with sweet juices, clothe with downy hair, Or hang, inshrined, their little orbs in air.

[_The myriad seeds_. l. 355. Nature would seem to have been wonderfully prodigal in the seeds of vegetables, and the spawn of fish; almost any one plant, if all its seeds should grow to maturity, would in a few years alone people the terrestrial globe. Mr. Ray asserts that 101 seeds of tobacco weighed only one grain, and that from one tobacco plant the seeds thus calculated amounted to 360,000! The seeds of the ferns are by him supposed to exceed a million on a leaf. As the works of nature are governed by general laws this exuberant reproduction prevents the accidental extinction of the species, at the same time that they serve for food for the higher orders of animation.

Every seed possesses a reservoir of nutriment designed for the growth of the future plant, this consists of starch, mucilage, or oil, within the coat of the seed, or of sugar and subacid pulp in the fruits, which belongs to it.

For the preservation of the immature seed nature has used many ingenious methods; some are wrapped in down, as the seeds of the rose, bean, and cotton-plant; others are suspended in a large air-vessel, as those of the bladder-sena, staphylaea, and pea.]

"So, late descry'd by HERSCHEL'S piercing sight, 360 Hang the bright squadrons of the twinkling Night; Ten thousand marshall'd stars, a silver zone, Effuse their blended lustres round her throne; Suns call to suns, in lucid clouds conspire, And light exterior skies with golden fire; 365 Resistless rolls the illimitable sphere, And one great circle forms the unmeasured year. --Roll on, YE STARS! exult in youthful prime, Mark with bright curves the printless steps of Time; Near and more near your beamy cars approach, 370 And lessening orbs on lessening orbs encroach;-- Flowers of the sky! ye too to age must yield, Frail as your silken sisters of the field! Star after star from Heaven's high arch shall rush, Suns sink on suns, and systems systems crush, 375 Headlong, extinct, to one dark centre fall, And Death and Night and Chaos mingle all! --Till o'er the wreck, emerging from the storm, Immortal NATURE lifts her changeful form, Mounts from her funeral pyre on wings of flame, 380 And soars and shines, another and the same.

[_And light exterior_. l. 364. I suspect this line is from Dwight's Conquest of Canaan, a poem written by a very young man, and which contains much fine versification.]

[_Near and more near_. l. 369. From the vacant spaces in some parts of the heavens, and the correspondent clusters of stars in their vicinity, Mr. Herschel concludes that the nebulae or constellations of fixed stars are approaching each other, and must finally coalesce in one mass. Phil. Trans. Vol. LXXV.]

[_Till o'er the wreck_. l. 377. The story of the phenix rising from its own ashes with a twinkling star upon its head, seems to have been an antient hieroglyphic emblem of the destruction and resuscitation of all things.

There is a figure of the great Platonic year with a phenix on his hand on the reverse of a medal of Adrian. Spence's Polym. p. 189.]

2. "Lo! on each SEED within its slender rind Life's golden threads in endless circles wind; Maze within maze the lucid webs are roll'd, And, as they burst, the living flame unfold. 385 The pulpy acorn, ere it swells, contains The Oak's vast branches in its milky veins; Each ravel'd bud, fine film, and fibre-line Traced with nice pencil on the small design. The young Narcissus, in it's bulb compress'd, 390 Cradles a second nestling on its breast; In whose fine arms a younger embryon lies, Folds its thin leaves, and shuts its floret-eyes; Grain within grain successive harvests dwell, And boundless forests slumber in a shell. 395 --So yon grey precipice, and ivy'd towers, Long winding meads, and intermingled bowers, Green files of poplars, o'er the lake that bow, And glimmering wheel, which rolls and foams below, In one bright point with nice distinction lie 400 Plan'd on the moving tablet of the eye. --So, fold on fold, Earth's wavy plains extend, And, sphere in sphere, its hidden strata bend;-- Incumbent Spring her beamy plumes expands O'er restless oceans, and impatient lands, 405 With genial lustres warms the mighty ball, And the GREAT SEED evolves, disclosing ALL; LIFE _buds_ or _breathes_ from Indus to the Poles, And the vast surface kindles, as it rolls!

[_Maze within maze_. l. 383. The elegant appearance on dissection of the young tulip in the bulb was first observed by Mariotte and is mentioned in the note on tulipa in Vol.II, and was afterwards noticed by Du Hamel. Acad. Scien. Lewenhook assures us that in the bud of a currant tree he could not only discover the ligneous part but even the berries themselves, appearing like small grapes. Chamb. Dict. art. Bud. Mr. Baker says he dissected a seed of trembling grass in which a perfect plant appeared with its root, sending forth two branches, from each of which several leaves or blades of grass proceeded. Microsc. Vol. I. p. 252. Mr. Bonnet saw four generations of successive plants in the bulb of a hyacinth. Bonnet Corps Organ. Vol. I. p. 103. Haller's Physiol. Vol. I. p. 91. In the terminal bud of a horse-chesnut the new flower may be seen by the naked eye covered with a mucilaginous down, and the same in the bulb of a narcissus, as I this morning observed in several of them sent me by Miss ---- for that purpose. Sept. 16.

Mr. Ferber speaks of the pleasure he received in observing in the buds of Hepatica and pedicularis hirsuta yet lying hid in the earth, and in the gems of the shrub daphne mezereon, and at the base of osmunda lunaria a perfect plant of the future year, discernable in all its parts a year before it comes forth, and in the seeds of nymphea nelumbo the leaves of the plant were seen so distinctly that the author found out by them what plant the seeds belonged to. The same of the seeds of the tulip tree or liriodendum tulipiferum. Amaen. Aced. Vol. VI.]

[_And the great seed_. l. 406. Alluding to the [Greek: proton oon], or first great egg of the antient philosophy, it had a serpent wrapped round it emblematical of divine wisdom, an image of it was afterwards preserved and worshipped in the temple of Dioscuri, and supposed to represent the egg of Leda. See a print of it in Bryant's Mythology. It was said to have been broken by the horns of the celestial bull, that is, it was hatched by the warmth of the Spring. See note on Canto I. l. 413.]

[_And the vast surface_. l. 408. L'Organization, le sentiment, le movement spontane, la vie, n'existent qu'a la surface de la terre, et dans le lieux exposes a la lumiere. Traite de Chymie par M. Lavoisier, Tom. I. p. 202.]

3. "Come, YE SOFT SYLPHS! who sport on Latian land, 410 Come, sweet-lip'd Zephyr, and Favonius bland! Teach the fine SEED, instinct with life, to shoot On Earth's cold bosom its descending root; With Pith elastic stretch its rising stem, Part the twin Lobes, expand the throbbing Gem; 415 Clasp in your airy arms the aspiring Plume, Fan with your balmy breath its kindling bloom, Each widening scale and bursting film unfold, Swell the green cup, and tint the flower with gold; While in bright veins the silvery Sap ascends, 420 And refluent blood in milky eddies bends; While, spread in air, the leaves respiring play, Or drink the golden quintessence of day. --So from his shell on Delta's shower-less isle Bursts into life the Monster of the Nile; 425 First in translucent lymph with cobweb-threads The Brain's fine floating tissue swells, and spreads; Nerve after nerve the glistening spine descends, The red Heart dances, the Aorta bends; Through each new gland the purple current glides, 430 New veins meandering drink the refluent tides; Edge over edge expands the hardening scale, And sheaths his slimy skin in silver mail. --Erewhile, emerging from the brooding sand, With Tyger-paw He prints the brineless strand, 435 High on the flood with speckled bosom swims, Helm'd with broad tail, and oar'd with giant limbs; Rolls his fierce eye-balls, clasps his iron claws, And champs with gnashing teeth his massy jaws; Old Nilus sighs along his cane-crown'd shores, 440 And swarthy Memphis trembles and adores.

[_Teach the fine seed_. l. 411. The seeds in their natural state fall on the surface of the earth, and having absorbed some moisture the root shoots itself downwards into the earth and the plume rises in air. Thus each endeavouring to seek its proper pabulum directed by a vegetable irritability similar to that of the lacteal system and to the lungs in animals.

The pith seems to push up or elongate the bud by its elasticity, like the pith in the callow quills of birds. This medulla Linneus believes to consist of a bundle of fibres, which diverging breaks through the bark yet gelatinous producing the buds.

The lobes are reservoirs of prepared nutriment for the young seed, which is absorbed by its placental vessels, and converted into sugar, till it has penetrated with its roots far enough into the earth to extract sufficient moisture, and has acquired leaves to convert it into nourishment. In some plants these lobes rise from the earth and supply the place of leaves, as in kidney-beans, cucumbers, and hence seem to serve both as a placenta to the foetus, and lungs to the young plant. During the process of germination the starch of the seed is converted into sugar, as is seen in the process of malting barley for the purpose of brewing. And is on this account very similar to the digestion of food in the stomachs of animals, which converts all their aliment into a chyle, which consists of mucilage, oil, and sugar; the placentation of buds will be spoken of hereafter.]

[_The silvery sap_. l. 419. See additional notes, No. XXXVI.]

[_Or drink the golden_. l. 422. Linneus having observed the great influence of light on vegetation, imagined that the leaves of plants inhaled electric matter from the light with their upper surface. (System of Vegetables translated, p. 8.)

The effect of light on plants occasions the actions of the vegetable muscles of their leaf-stalks, which turn the upper side of the leaf to the light, and which open their calyxes and chorols, according to the experiments of Abbe Tessier, who exposed variety of plants in a cavern to different quantities of light. Hist. de L'Academie Royal. Ann. 1783. The sleep or vigilance of plants seems owing to the presence or absence of this stimulus. See note on Nimosa, Vol. II.]

XI. "Come, YE SOFT SYLPHS! who fan the Paphian groves, And bear on sportive wings the callow Loves; Call with sweet whisper, in each gale that blows, The slumbering Snow-drop from her long repose; 445 Charm the pale Primrose from her clay-cold bed, Unveil the bashful Violet's tremulous head; While from her bud the playful Tulip breaks, And young Carnations peep with blushing cheeks; Bid the closed _Petals_ from nocturnal cold 450 The virgin _Style_ in silken curtains fold, Shake into viewless air the morning dews, And wave in light their iridescent hues; While from on high the bursting _Anthers_ trust To the mild breezes their prolific dust; 455 Or bend in rapture o'er the central Fair, Love out their hour, and leave their lives in air. So in his silken sepulchre the Worm, Warm'd with new life, unfolds his larva-form; Erewhile aloft in wanton circles moves, 460 And woos on Hymen-wings his velvet loves.

[_Love out their hour_. l. 456. The vegetable passion of love is agreeably seen in the flower of the parnassia, in which the males alternately approach and recede from the female, and in the flower of nigella, or devil in the bush, in which the tall females bend down to their dwarf husbands. But I was this morning surprised to observe, amongst Sir Brooke Boothby's valuable collection of plants at Ashbourn, the manifest adultery of several females of the plant Collinsonia, who had bent themselves into contact with the males of other flowers of the same plant in their vicinity, neglectful of their own. Sept. 16. See additional notes, No. XXXVIII.]

[_Unfolds his larva-form_. l. 458. The flower bursts forth from its larva, the herb, naked and perfect like a butterfly from its chrysolis; winged with its corol; wing-sheathed by its calyx; consisting alone of the organs of reproduction. The males, or stamens, have their anthers replete with a prolific powder containing the vivifying fovilla: in the females, or pistils, exists the ovary, terminated by the tubular stigma. When the anthers burst and shed their bags of dust, the male fovilla is received by the prolific lymph of the stigma, and produces the seed or egg, which is nourished in the ovary. System of Vegetables translated from Linneus by the Lichfield Society, p. 10.]

XII. 1. "If prouder branches with exuberance rude Point their green gems, their barren shoots protrude; Wound them, ye SYLPHS! with little knives, or bind A wiry ringlet round the swelling rind; 465 Bisect with chissel fine the root below, Or bend to earth the inhospitable bough. So shall each germ with new prolific power Delay the leaf-bud, and expand the flower; Closed in the _Style_ the tender pith shall end, 470 The lengthening Wood in circling _Stamens_ bend; The smoother Rind its soft embroidery spread In vaulted _Petals_ o'er their fertile bed; While the rough Bark, in circling mazes roll'd, Forms the green _Cup_ with many a wrinkled fold; 475 And each small bud-scale spreads its foliage hard, Firm round the callow germ, a _Floral Guard_.

[_Wound them, ye Sylphs!_ l. 463. Mr. Whitmill advised to bind some of the most vigorous shoots with strong wire, and even some of the large roots; and Mr. Warner cuts, what he calls a wild worm about the body of the tree, or scores the bark quite to the wood like a screw with a sharp knife. Bradley on Gardening, Vol. II. p. 155. Mr. Fitzgerald produced flowers and fruit on wall trees by cutting off a part of the bark. Phil. Trans. Ann. 1761. M. Buffon produced the same effect by a straight bandage put round a branch, Act. Paris, Ann. 1738, and concludes that an ingrafted branch bears better from its vessels being compressed by the callous.

A compleat cylinder of the bark about an inch in height was cut off from the branch of a pear tree against a wall in Mr. Howard's garden at Lichfield about five years ago, the circumcised part is now not above half the diameter of the branch above and below it, yet this branch has been full of fruit every year since, when the other branches of the tree bore only sparingly. I lately observed that the leaves of this wounded branch were smaller and paler, and the fruit less in size, and ripened sooner than on the other parts of the tree. Another branch has the bark taken off not quite all round with much the same effect.

The theory of this curious vegetable fact has been esteemed difficult, but receives great light from the foregoing account of the individuality of buds. A flower-bud dies, when it has perfected its seed, like an annual plant, and hence requires no place on the bark for new roots to pass downwards; but on the contrary leaf-buds, as they advance into shoots, form new buds in the axilla of every leaf, which new buds require new roots to pass down the bark, and thus thicken as well as elongate the branch, now if a wire or string be tied round the bark, many of these new roots cannot descend, and thence more of the buds will be converted into flower-buds.

It is customary to debark oak-trees in the spring, which are intended to be felled in the ensuing autumn; because the bark comes off easier at this season, and the sap-wood, or alburnum, is believed to become harder and more durable, if the tree remains till the end of summer. The trees thus stripped of their bark put forth shoots as usual with acorns on the 6th 7th and 8th joint, like vines; but in the branches I examined, the joints of the debarked trees were much shorter than those of other oak- trees; the acorns were more numerous; and no new buds were produced above the joints which bore acorns. From hence it appears that the branches of debarked oak-trees produce fewer leaf-buds, and more flower- buds, which last circumstance I suppose must depend on their being sooner or later debarked in the vernal months. And, secondly, that the new buds of debarked oak-trees continue to obtain moisture from the alburnum after the season of the ascent of sap in other vegetables ceases; which in this unnatural state of the debarked tree may act as capillary tubes, like the alburnum of the small debarked cylinder of a pear-tree abovementioned; or may continue to act as placental vessels, as happens to the animal embryon in cases of superfetation; when the fetus continues a month or two in the womb beyond its usual time, of which some instances have been recorded, the placenta continues to supply perhaps the double office both of nutrition and of respiration.]

[_And bend to earth_. l. 466. Mr. Hitt in his treatise on fruit trees observes that if a vigorous branch of a wall tree be bent to the horizon, or beneath it, it looses its vigour and becomes a bearing branch. The theory of this I suppose to depend on the difficulty with which the leaf-shoots can protrude the roots necessary for their new progeny of buds upwards along the bended branch to the earth contrary to their natural habits or powers, whence more flower-shoots are produced which do not require new roots to pass along the bark of the bended branch, but which let their offspring, the seeds, fall upon the earth and seek roots for themselves.]

[_With new prolific power_. l. 467. About Midsummer the new buds are formed, but it is believed by some of the Linnean school, that these buds may in their early state be either converted into flower-buds or leaf-buds according to the vigour of the vegetating branch. Thus if the upper part of a branch be cut away, the buds near the extremity of the remaining stem, having a greater proportional supply of nutriment, or possessing a greater facility of shooting their roots, or absorbent vessels, down the bark, will become leaf-buds, which might otherwise have been flower-buds. And the contrary as explained in note on l. 463. of this Canto.]

[_Closed in the style_. l. 469. "I conceive the medulla of a plant to consist of a bundle of nervous fibres, and that the propelling vital power separates their uppermost extremities. These, diverging, penetrate the bark, which is now gelatinous, and become multiplied in the new gem, or leaf-bud. The ascending vessels of the bark being thus divided by the nervous fibres, which perforate it, and the ascent of its fluids being thus impeded, the bark is extended into a leaf. But the flower is produced, when the protrusion of the medulla is greater than the retention of the including cortical part; whence the substance of the bark is expanded in the calyx; that of the rind, (or interior bark,) in the corol; that of the wood in the stamens, that of the medulla in the pistil. Vegetation thus terminates in the production of new life, the ultimate medullary and cortical fibres being collected in the seeds." Linnei Systema Veget. p. 6. edit. 14.]

2. "Where cruder juices swell the leafy vein, Stint the young germ, the tender blossom stain; On each lop'd shoot a softer scion bind, 480 Pith press'd to pith, and rind applied to rind, So shall the trunk with loftier crest ascend, And wide in air its happier arms extend; Nurse the new buds, admire the leaves unknown, And blushing bend with fruitage not its own.

[_Nurse the new buds_. l. 483. Mr. Fairchild budded a passion-tree, whose leaves were spotted with yellow, into one which bears long fruit. The buds did not take, nevertheless in a fortnight yellow spots began to shew themselves about three feet above the inoculation, and in a short time afterwards yellow spots appeared on a shoot which came out of the ground from another part of the plant. Bradley, Vol. II. p. 129. These facts are the more curious since from experiments of ingrafting red currants on black (Ib. Vol. II.) the fruit does not acquire any change of flavour, and by many other experiments neither colour nor any other change is produced in the fruit ingrafted on other stocks.

There is an apple described in Bradley's work which is said to have one side of it a sweet fruit which boils soft, and the other side a sour fruit which boils hard, which Mr. Bradley so long ago as the year 1721 ingeniously ascribes to the farina of one of these apples impregnating the other, which would seem the more probable if we consider that each division of an apple is a separate womb, and may therefore have a separate impregnation like puppies of different kinds in one litter. The same is said to have occurred in oranges and lemons, and grapes of different colours.]

485 "Thus when in holy triumph Aaron trod, And offer'd on the shrine his mystic rod; First a new bark its silken tissue weaves, New buds emerging widen into leaves; Fair fruits protrude, enascent flowers expand, 490 And blush and tremble round the living wand.

XIII. 1. "SYLPHS! on each Oak-bud wound the wormy galls, With pigmy spears, or crush the venom'd balls; Fright the green Locust from his foamy bed, Unweave the Caterpillar's gluey thread; 495 Chase the fierce Earwig, scare the bloated Toad, Arrest the snail upon his slimy road; Arm with sharp thorns the Sweet-brier's tender wood, And dash the Cynips from her damask bud; Steep in ambrosial dews the Woodbine's bells, 500 And drive the Night-moth from her honey'd cells. So where the Humming-bird in Chili's bowers On murmuring pinions robs the pendent flowers; Seeks, where fine pores their dulcet balm distill, And sucks the treasure with proboscis-bill; 505 Fair CYPREPEDIA with successful guile Knits her smooth brow, extinguishes her smile; A Spiders bloated paunch and jointed arms Hide her fine form, and mask her blushing charms; In ambush sly the mimic warrior lies, 510 And on quick wing the panting plunderer flies.

[_Fair Cyprepedia_. l. 505. The cyprepedium from South America is supposed to be of larger size and brighter colours than that from North America from which this print is taken; it has a large globular nectary about the size of a pidgeon's egg of a fleshy colour, and an incision or depression on its upper part, much resembling the body of the large American spider; this globular nectary is attached to divergent slender petals not unlike the legs of the same animal. This spider is called by Linneus Arenea avicularia, with a convex orbicular thorax, the center transversely excavated, he adds that it catches small birds as well as insects, and has the venemous bite of a serpent. System Nature, Tom. I. p. 1034. M. Lonvilliers de Poincy, (Histoire Nat. des Antilles, Cap. xiv. art. III.) calls it Phalange, and describes the body to be the size of a pidgeon's egg, with a hollow on its back like a navel, and mentions its catching the humming-bird in its strong nets.

The similitude of this flower to this great spider seems to be a vegetable contrivance to prevent the humming-bird from plundering its honey. About Matlock in Derbyshire the fly-ophris is produced, the nectary of which so much resembles the small wall-bee, perhaps the apis ichneumonea, that it may be easily mistaken for it at a small distance. It is probable that by this means it may often escape being plundered. See note on lonicera in the next poem.

A bird of our own country called a willow-wren (Motacilla) runs up the stem of the crown-imperial (Frittillaria coronalis) and sips the pendulous drops within its petals. This species of Motacilla is called by Ray Regulus non cristatus. White's Hist. of Selborne.]

[Illustration: _Cypripedium. London, Published Dec'r 1st 1791 by J. Johnson, St. Paul's Church Yard._]

2. "Shield the young Harvest from devouring blight, The Smut's dark poison, and the Mildew white; Deep-rooted Mould, and Ergot's horn uncouth, And break the Canker's desolating tooth. 515 First in one point the festering wound confin'd Mines unperceived beneath the shrivel'd rin'd; Then climbs the branches with increasing strength, Spreads as they spread, and lengthens with their length; --Thus the slight wound ingraved on glass unneal'd 520 Runs in white lines along the lucid field; Crack follows crack, to laws elastic just, And the frail fabric shivers into dust.

[_Shield the young harvest_. l. 511. Linneus enumerates but four diseases of plants; Erysyche, the white mucor or mould, with sessile tawny heads, with which the leaves are sprinkled, as is frequent on the hop, humulus, maple, acer, &c. Rubigo, the ferrugineous powder sprinkled under the leaves frequent in lady's mantle, alchemilla, &c.

Clavus, when the seeds grow out into larger horns black without, as in rye. This is called Ergot by the french writers.

Ustulago, when the fruit instead of seed produces a black powder, as in barley, oats, &c. To which perhaps the honey-dew ought to have been added, and the canker, in the former of which the nourishing fluid of the plant seems to be exsuded by a retrograde motion of the cutaneous lymphatics, as in the sweating sickness of the last century. The latter is a phagedenic ulcer of the bark, very destructive to young apple- trees, and which in cherry-trees is attended with a deposition of gum arabic, which often terminates in the death of the tree.]

[_Ergot's horn_. l. 513. There is a disease frequently affects the rye in France, and sometimes in England in moist seasons, which is called Ergot, or horn seed; the grain becomes considerably elongated and is either straight or crooked, containing black meal along with the white, and appears to be pierced by insects, which were probably the cause of the disease. Mr. Duhamel ascribes it to this cause, and compares it to galls on oak-leaves. By the use of this bad grain amongst the poor diseases have been produced attended with great debility and mortification of the extremities both in France and England. Dict. Raison. art. Siegle. Philosop. Transact.]

[_On glass unneal'd_. l. 519. The glass makers occasionally make what they call _proofs_, which are cooled hastily, whereas the other glass vessels are removed from warmer ovens to cooler ones, and suffered to cool by slow degrees, which is called annealing, or nealing them. If an unnealed glass be scratched by even a grain of sand falling into it, it will seem to consider of it for some time, or even a day, and will then crack into a thousand pieces.

The same happens to a smooth surfaced lead-ore in Derbyshire, the workmen having cleared a large face of it scratch it with picks, and in a few hours many tons of it crack to pieces and fall, with a kind of explosion. Whitehurst's Theory of Earth.

Glass dropped into cold water, called Prince Rupert's drops, explode when a small part of their tails are broken off, more suddenly indeed, but probably from the same cause. Are the internal particles of these elastic bodies kept so far from each other by the external crust that they are nearly in a state of repulsion into which state they are thrown by their vibrations from any violence applied? Or, like elastic balls in certain proportions suspended in contact with each other, can motion once began be increased by their elasticity, till the whole explodes? And can this power be applied to any mechanical purposes?]

XIV. I. "SYLPHS! if with morn destructive Eurus springs, O, clasp the Harebel with your velvet wings; 525 Screen with thick leaves the Jasmine as it blows, And shake the white rime from the shuddering Rose; Whilst Amaryllis turns with graceful ease Her blushing beauties, and eludes the breeze.-- SYLPHS! if at noon the Fritillary droops, 530 With drops nectareous hang her nodding cups; Thin clouds of Gossamer in air display, And hide the vale's chaste Lily from the ray; Whilst Erythrina o'er her tender flower Bends all her leaves, and braves the sultry hour;-- 535 Shield, when cold Hesper sheds his dewy light, Mimosa's soft sensations from the night; Fold her thin foilage, close her timid flowers, And with ambrosial slumbers guard her bowers; O'er each warm wall while Cerea flings her arms, 540 And wastes on night's dull eye a blaze of charms.

[Illustration: _Erythrina Corallodendron. London Published Dec'r 1st by J. Johnson St. Paul's Church Yard._]

[_With ambrosial slumbers_. l. 538. Many vegetables during the night do not seem to respire, but to sleep like the dormant animals and insects in winter. This appears from the mimosa and many other plants closing the upper sides of their leaves together in their sleep, and thus precluding that side of them from both light and air. And from many flowers closing up the polished or interior side of their petals, which we have also endeavoured to shew to be a respiratory organ.

The irritability of plants is abundantly evinced by the absorption and pulmonary circulation of their juices; their sensibility is shewn by the approaches of the males to the females, and of the females to the males in numerous instances; and, as the essential circumstance of sleep consists in the temporary abolition of voluntary power alone, the sleep of plants evinces that they possess voluntary power; which also indisputably appears in many of them by closing their petals or their leaves during cold, or rain, or darkness, or from mechanic violence.]

2. Round her tall Elm with dewy fingers twine The gadding tendrils of the adventurous Vine; From arm to arm in gay festoons suspend Her fragrant flowers, her graceful foliage bend; 545 Swell with sweet juice her vermil orbs, and feed Shrined in transparent pulp her pearly seed; Hang round the Orange all her silver bells, And guard her fragrance with Hesperian spells; Bud after bud her polish'd leaves unfold, 550 And load her branches with successive gold. So the learn'd Alchemist exulting sees Rise in his bright matrass DIANA'S trees; Drop after drop, with just delay he pours The red-fumed acid on Potosi's ores; 555 With sudden flash the fierce bullitions rise, And wide in air the gas phlogistic flies; Slow shoot, at length, in many a brilliant mass Metallic roots across the netted glass; Branch after branch extend their silver stems, 560 Bud into gold, and blossoms into gems.

[_Diana's trees_, l. 552. The chemists and astronomers from the earliest antiquity have used the same characters to represent the metals and the planets, which were most probably outlines or abstracts of the original hieroglyphic figures of Egypt. These afterwards acquired niches in their temples, and represented Gods as well as metals and planets; whence silver is called Diana, or the moon, in the books of alchemy.

The process for making Diana's silver tree is thus described by Lemeri. Dissolve one ounce of pure silver in acid of nitre very pure and moderately strong; mix this solution with about twenty ounces of distilled water; add to this two ounces of mercury, and let it remain at rest. In about four days there will form upon the mercury a tree of silver with branches imitating vegetation.

1. As the mercury has a greater affinity than silver with the nitrous acid, the silver becomes precipitated; and, being deprived of the nitrous oxygene by the mercury, sinks down in its metallic form and lustre. 2. The attraction between silver and mercury, which causes them readily to amalgamate together, occasions the precipitated silver to adhere to the surface of the mercury in preference to any other part of the vessel. 3. The attraction of the particles of the precipitated silver to each other causes the beginning branches to thicken and elongate into trees and shrubs rooted on the mercury. For other circumstances concerning this beautiful experiment see Mr. Keir's Chemical Dictionary, art. Arbor Dianae; a work perhaps of greater utility to mankind than the lost Alexandrian Library; the continuation of which is so eagerly expected by all, who are occupied in the arts, or attached to the sciences.]

So sits enthron'd in vegetable pride Imperial KEW by Thames's glittering side; Obedient sails from realms unfurrow'd bring For her the unnam'd progeny of spring; 565 Attendant Nymphs her dulcet mandates hear, And nurse in fostering arms the tender year, Plant the young bulb, inhume the living seed, Prop the weak stem, the erring tendril lead; Or fan in glass-built fanes the stranger flowers 570 With milder gales, and steep with warmer showers. Delighted Thames through tropic umbrage glides, And flowers antarctic, bending o'er his tides; Drinks the new tints, the sweets unknown inhales, And calls the sons of science to his vales. 575 In one bright point admiring Nature eyes The fruits and foliage of discordant skies, Twines the gay floret with the fragrant bough, And bends the wreath round GEORGE'S royal brow. --Sometimes retiring, from the public weal 580 One tranquil hour the ROYAL PARTNERS steal; Through glades exotic pass with step sublime, Or mark the growths of Britain's happier clime; With beauty blossom'd, and with virtue blaz'd, Mark the fair Scions, that themselves have rais'd; 585 Sweet blooms the Rose, the towering Oak expands, The Grace and Guard of Britain's golden lands.

XV. SYLPHS! who, round earth on purple pinions borne, Attend the radiant chariot of the morn; Lead the gay hours along the ethereal hight, 590 And on each dun meridian shower the light; SYLPHS! who from realms of equatorial day To climes, that shudder in the polar ray, From zone to zone pursue on shifting wing, The bright perennial journey of the spring; 595 Bring my rich Balms from Mecca's hallow'd glades, Sweet flowers, that glitter in Arabia's shades; Fruits, whose fair forms in bright succession glow Gilding the Banks of Arno, or of Po; Each leaf, whose fragrant steam with ruby lip 600 Gay China's nymphs from pictur'd vases sip; Each spicy rind, which sultry India boasts, Scenting the night-air round her breezy coasts; Roots whose bold stems in bleak Siberia blow, And gem with many a tint the eternal snow; 605 Barks, whose broad umbrage high in ether waves O'er Ande's steeps, and hides his golden caves; --And, where yon oak extends his dusky shoots Wide o'er the rill, that bubbles from his roots; Beneath whose arms, protected from the storm 610 A turf-built altar rears it's rustic form; SYLPHS! with religious hands fresh garlands twine, And deck with lavish pomp HYGEIA'S shrine.

"Call with loud voice the Sisterhood, that dwell On floating cloud, wide wave, or bubbling well; 615 Stamp with charm'd foot, convoke the alarmed Gnomes From golden beds, and adamantine domes; Each from her sphere with beckoning arm invite, Curl'd with red flame, the Vestal Forms of light. Close all your spotted wings, in lucid ranks 620 Press with your bending knees the crowded banks, Cross your meek arms, incline your wreathed brows, And win the Goddess with unwearied vows.

"Oh, wave, HYGEIA! o'er BRITANNIA'S throne Thy serpent-wand, and mark it for thy own; 625 Lead round her breezy coasts thy guardian trains, Her nodding forests, and her waving plains; Shed o'er her peopled realms thy beamy smile, And with thy airy temple crown her isle!"

The GODDESS ceased,--and calling from afar 630 The wandering Zephyrs, joins them to her car; Mounts with light bound, and graceful, as she bends, Whirls the long lash, the flexile rein extends; On whispering wheels the silver axle slides, Climbs into air, and cleaves the crystal tides; 635 Burst from its pearly chains, her amber hair Streams o'er her ivory shoulders, buoy'd in air; Swells her white veil, with ruby clasp confined Round her fair brow, and undulates behind; The lessening coursers rise in spiral rings, 640 Pierce the slow-sailing clouds, and stretch their shadowy wings.

CONTENTS

OF

THE NOTES.

CANTO I.

Rosicrucian machinery. 73

All bodies are immersed in the matter of heat. Particles of bodies do not touch each other. 97

Gradual progress of the formation of the earth, and of plants and animals. Monstrous births 101

Fixed stars approach towards each other, they were projected from chaos by explosion, and the planets projected from them 105

An atmosphere of inflammable air above the common atmosphere principally about the poles 123

Twilight fifty miles high. Wants further observations 126

Immediate cause of volcanos from steam and other vapours. They prevent greater earthquakes 152

Conductors of heat. Cold on the tops of mountains 176

Phosphorescent light in the evening from all bodies 177

Phosphoric light from calcined shells. Bolognian stone. Experiments of Beccari and Wilson 182

Ignis fatuus doubtful 189

Electric Eel. Its electric organs. Compared to the electric Leyden phial 202

Discovery of fire. Tools of steel. Forests subdued. Quantity of food increased by cookery 212

Medusa originally an hieroglyphic of divine wisdom 218

Cause of explosions from combined heat. Heat given out from air in respiration. Oxygene looses less heat when converted into nitrous acid than in any other of its combinations 226

Sparks from the collision of flints are electric. From the collision of flint and steel are from the combustion of the steel 229

Gunpowder described by Bacon. Its power. Should be lighted in the centre. A new kind of it. Levels the weak and strong 242

Steam-engine invented by Savery. Improved by Newcomen. Perfected by Watt and Boulton 254

Divine benevolence. The parts of nature not of equal excellence 278

Mr. Boulton's steam-engine for the purpose of coining would save many lives from the executioner 281

Labours of Hercules of great antiquity. Pillars of Hercules. Surface of the Mediteranean lower than the Atlantic. Abyla and Calpe. Flood of Deucalion 297

Accumulation of electricity not from friction 335

Mr. Bennet's sensible electrometer 345

Halo of saints is pictorial language 358

We have a sense adapted to perceive heat but not electricity 365

Paralytic limbs move by electric influence 367

Death of Professor Richman by electricity 373

Lightning drawn from the clouds. How to be safe in thunder storms 383

Animal heat from air in respiration. Perpetual necessity of respiration. Spirit of animation perpetually renewed 401

Cupid rises from the egg of night. Mrs. Cosway's painting of this subject 413

Western-winds. Their origin. Warmer than south-winds. Produce a thaw 430

Water expands in freezing. Destroys succulent plants, not resinous ones. Trees in valleys more liable to injury. Fig-trees bent to the ground in winter 439

Buds and bulbs are the winter cradle of the plant. Defended from frost and from insects. Tulip produces one flower-bulb and several leaf-bulbs, and perishes. 460

Matter of heat is different from light. Vegetables blanched by exclusion of light. Turn the upper surface of their leaves to the light. Water decomposed as it escapes from their pores. Hence vegetables purify air in the day time only. 462

Electricity forwards the growth of plants. Silk-worms electrised spin sooner. Water decomposed in vegetables, and by electricity 463

Sympathetic inks which appear by heat, and disappear in the cold. Made from cobalt 487

Star in Cassiope's chair 515

Ice-islands 100 fathoms deep. Sea-ice more difficult of solution. Ice evaporates producing great cold. Ice-islands increase. Should be navigated into southern climates. Some ice-islands have floated southwards 60 miles long. Steam attending them in warm climates 529

Monsoon cools the sands of Abyssinia 547

Ascending vapours are electrised plus, as appears from an experiment of Mr. Bennet. Electricity supports vapour in clouds. Thunder showers from combination of inflammable and vital airs 553

CANTO II.

Solar volcanos analogous to terrestrial and lunar ones. Spots of the sun are excavations 14

Spherical form of the earth. Ocean from condensed vapour. Character of Mr. Whitehurst 17

Granite the oldest part of the earth. Then limestone. And lastly, clay, iron, coal, sandstone. Three great concentric divisions of the globe 35

Formation of primeval islands before the production of the moon. Paradise. The Golden Age. Rain-bow. Water of the sea originally fresh 36

Venus rising from the sea an hieroglyphic emblem of the production of the earth beneath the ocean 47

First great volcanos in the central parts of the earth. From steam, inflammable gas, and vital air. Present volcanos like mole-hills 68

Moon has little or no atmosphere. Its ocean is frozen. Is not yet inhabited, but may be in time 82

Earth's axis changed by the ascent of the moon. Its diurnal motion retarded. One great tide 84

Limestone produced from shells. Spars with double refractions. Marble. Chalk 93

Antient statues of Hercules. Antinous. Apollo. Venus. Designs of Roubiliac. Monument of General Wade. Statues of Mrs. Damer 101

Morasses rest on limestone. Of immense extent 116

Salts from animal and vegetable bodies decompose each other, except marine salt. Salt mines in Poland. Timber does not decay in them. Rock- salt produced by evaporation from sea-water. Fossil shells in salt mines. Salt in hollow pyramids. In cubes. Sea-water contains about one- thirtieth of salt 119

Nitre, native in Bengal and Italy. Nitrous gas combined with vital air produces red clouds, and the two airs occupy less space than one of them before, and give out heat. Oxygene and azote produce nitrous acid 143

Iron from decomposed vegetables. Chalybeat springs. Fern-leaves in nodules of iron. Concentric spheres of iron nodules owing to polarity, like iron-filings arranged by a magnet. Great strata of the earth owing to their polarity 183

Hardness of steel for tools. Gave superiority to the European nations. Welding of steel. Its magnetism. Uses of gold 192

Artificial magnets improved by Savery and Dr. Knight, perfected by Mr. Michel. How produced. Polarity owing to the earth's rotatory motion. The electric fluid, and the matter of heat, and magnetism gravitate on each other. Magnetism being the lightest is found nearest the axis of the motion. Electricity produces northern lights by its centrifugal motion 193

Acids from vegetable recrements. Flint has its acid from the new world. Its base in part from the old world, and in part from the new. Precious stones 215

Diamond. Its great refraction of light. Its volatibility by heat. If an inflammable body. 228

Fires of the new world from fermentation. Whence sulphur and bitumen by sublimation, the clay, coal, and flint remaining 275

Colours not distinguishable in the enamel-kiln, till a bit of dry wood is introduced 283

Etrurian pottery prior to the foundations of Rome. Excelled in fine forms, and in a non-vitreous encaustic painting, which was lost till restored by Mr. Wedgwood. Still influences the taste of the inhabitants 291

Mr. Wedgwood's cameo of a slave in chains, and of Hope 315

Basso-relievos of two or more colours not made by the antients. Invented by Mr. Wedgwood 342

Petroleum and naptha have been sublimed. Whence jet and amber. They absorb air. Attract straws when rubbed. Electricity from electron the greek name for amber 353

Clefts in granite rocks in which metals are found. Iron and manganese found in all vegetables. Manganese in limestone. Warm springs from steam rising up the clefts of granite and limestone. Ponderous earth in limestone clefts and in granite. Copper, lead, iron, from descending materials. High mountains of granite contain no ores near their summits. Transmutation of metals. Of lead into calamy. Into silver 398

Armies of Cambytes destroyed by famine, and by sand-storms 435

Whirling turrets of sand described and explained 478

Granite shews iron as it decomposes. Marble decomposes. Immense quantity of charcoal exists in limestone. Volcanic slags decompose, and become clay 523

Millstones raised by wooden pegs 524

Hannibal made a passage by fire over the Alps 534

Passed tense of many words twofold, as driven or drove, spoken or spoke. A poetic licence 609

CANTO III.

Clouds consist of aqueous spheres, which do not easily unite, like globules of quicksilver, as may be seen in riding through water. Owing to electricity. Snow. Hailstones rounded by attrition and dissolution of their angles. Not from frozen drops of water 15

Dew on points and edges of grass, or hangs over cabbage-leaves, needle floats on water 18

Mists over rivers and on mountains. Halo round the moon. Shadow of a church-steeple upon a mist. Dry mist, or want of transparency of the air, a sign of fair-weather 20

Tides on both sides of the earth. Moon's tides should be much greater than the earth's tides. The ocean of the moon is frozen 61

Spiral form of shells saves calcareous matter. Serves them as an organ of hearing. Calcareous matter produced from inflamed membranes. Colours of shells, labradore-stone from mother-pearl. Fossil shells not now found recent 66

Sea-insects like flowers. Actinia 82

Production of pearls, not a disease of the fish. Crab's eyes. Reservoirs of pearly matter 84

Rocks of coral in the south-sea. Coralloid limestone at Linsel, and Coalbrook Dale 90

Rocks thrown from mountains, ice from glaciers, and portions of earth, or morasses, removed by columns of water. Earth-motion in Shropshire. Water of wells rising above the level of the ground. St. Alkmond's well near Derby might be raised many yards, so as to serve the town. Well at Sheerness, and at Hartford in Connecticut 116

Moonsoons attended with rain Overflowing of the Nile. Vortex of ascending air. Rising of the Dogstar announces the floods of the Nile. Anubis hung out upon their temples 129

Situations exempt from rain. At the Line in Lower Egypt. On the coast of Peru 138

Giesar, a boiling fountain in Iceland. Water with great degrees of heat dissolves siliceous matter. Earthquake from steam 150

Warm springs not from decomposed pyrites. From steam rising up fissures from great depths 166

Buxton bath possesses 82 degrees of heat. Is improperly called a warm bath. A chill at immersion, and then a sensation of warmth, like the eye in an obscure room owing to increased sensibility of the skin 184

Water compounded of pure air and inflammable air with as much matter of heat as preserves it fluid. Perpetually decomposed by vegetables in the sun's light, and recomposed in the atmosphere 204

Mythological interpretation of Jupiter and Juno designed as an emblem of the composition of water from two airs 260

Death of Mrs. French 308

Tomb of Mr. Brindley 341

Invention of the pump. The piston lifts the atmosphere above it. The surrounding atmosphere presses up the water into the vacuum. Manner in which a child sucks 366

Air-cell in engines for extinguishing fire. Water dispersed by the explosion of Gunpowder. Houses preserved from fire by earth on the floors, by a second ceiling of iron-plates or coarse mortar. Wood impregnated with alabaster or flint 406

Muscular actions and sensations of plants 460

River Achelous. Horn of Plenty 495

Flooding lands defends them from vernal frosts. Some springs deposit calcareous earth. Some contain azotic gas, which contributes to produce nitre. Snow water less serviceable 540

CANTO IV.

Cacalia produces much honey, that a part may be taken by insects without injury 2

Analysis of common air. Source of azote. Of Oxygene. Water decomposed by vegetable pores and the sun's light. Blood gives out phlogiston and receives vital air. Acquires heat and the vivifying principle 34

Cupid and Psyche 48

Simoom, a pestilential wind. Described. Owing to volcanic electricity. Not a whirlwind 65

Contagion either animal or vegetable 82

Thyrsis escapes the Plague 91

Barometer and air-pump, Dew on exhausting the receiver though the hygrometer points to dryness. Rare air will dissolve or acquire more heat, and more moisture, and more electricity 128

Sound propagated best by dense bodies, as wood, and water, and earth. Fish in spiral shells all ear 164

Discoveries of Dr. Priestley. Green vegetable matter. Pure air contained in the calces of metals, as minium, manganese, calamy, ochre 166

Fable of Proserpine an antient chemical emblem 178

Diving balloons supplied with pure air from minium. Account of one by Mr. Boyle 195

Mr. Day. Mr. Spalding 217

Captain Pierce and his daughters 219

Pestilential winds of volcanic origin. Jordan flows through a country of volcanos 294

Change of wind owing to small causes. If the wind could be governed, the products of the earth would be doubled, and its number of inhabitants increased 308

Mr. Kirwan's treatise on temperature of climates 342

Seeds of plants. Spawn of fish. Nutriment lodged in seeds. Their preservation in their seed-vessels 355

Fixed stars approach each other 369

Fable of the Phoenix 377

Plants visible within bulbs, and buds, and seeds 383

Great Egg of Night 406

Seeds shoot into the ground. Pith. Seed-lobes. Starch converted into sugar. Like animal chyle 411

Light occasions the actions of vegetable muscles. Keeps them awake 422

Vegetable love in Parnassia, Nigella. Vegetable adultery in Collinsonia 456

Strong vegetable shoots and roots bound with wire, in part debarked, whence leaf-buds converted into flower-buds. Theory of this curious fact 463

Branches bent to the horizon bear more fruit 466

Engrafting of a spotted passion-flower produced spots upon the stock. Apple soft on one side and hard on the other 483

Cyprepedium assumes the form of a large spider to affright the humming- bird. Fly-ophris. Willow-wren sucks the honey of the crown-imperial 505

Diseases of plants four kinds. Honey-dew 511

Ergot a disease of rye 513

Glass unannealed. Its cracks owing to elasticity. One kind of lead-ore cracks into pieces. Prince Rupert's drops. Elastic balls 519

Sleep of plants. Their irritability, sensibility, and voluntary motions 538

ADDITIONAL NOTES.

NOTE I.--METEORS.

_Etherial Forms! you chase the shooting stars, Or yoke the vollied lightnings to your cars._

CANTO I. l. 115.

There seem to be three concentric strata of our incumbent atmosphere; in which, or between them, are produced four kinds of meteors; lightning, shooting stars, fire-balls, and northern lights. First, the lower region of air, or that which is dense enough to resist by the adhesion of its particles the descent of condensed vapour, or clouds, which may extend from one to three or four miles high. In this region the common lightning is produced from the accumulation or defect of electric matter in those floating fields of vapour either in respect to each other, or in respect to the earth beneath them, or the dissolved vapour above them, which is constantly varying both with the change of the form of the clouds, which thus evolve a greater or less surface; and also with their ever-changing degree of condensation. As the lightning is thus produced in dense air, it proceeds but a short course on account of the greater resistance which it encounters, is attended with a loud explosion, and appears with a red light.

2. The second region of the atmosphere I suppose to be that which has too little tenacity to support condensed vapour or clouds; but which yet contains invisible vapour, or water in aerial solution. This aerial solution of water differs from that dissolved in the matter of heat, as it is supported by its adhesion to the particles of air, and is not precipitated by cold. In this stratum it seems probable that the meteors called shooting stars are produced; and that they consist of electric sparks, or lightning, passing from one region to another of these invisible fields of aero-aqueous solution. The height of these shooting stars has not yet been ascertained by sufficient observation; Dr. Blagden thinks their situation is lower down in the atmosphere than that of fireballs, which he conjectures from their swift apparent motion, and ascribes their smallness to the more minute division of the electric matter of which they are supposed to consist, owing to the greater resistance of the denser medium through which they pass, than that in which the fire-balls exist. Mr. Brydone observed that the shooting stars appeared to him to be as high in the atmosphere, when he was near the summit of mount Etna, as they do when observed from the plain. Phil. Tran. Vol. LXIII.

As the stratum of air, in which shooting stars are supposed to exist is much rarer than that in which lightning resides, and yet much denser than that in which fire-balls are produced, they will be attracted at a greater distance than the former, and at a less than the latter. From this rarity of the air so small a sound will be produced by their explosion, as not to reach the lower parts of the atmosphere; their quantity of light from their greater distance being small, is never seen through dense air at all, and thence does not appear red, like lightning or fire balls. There are no apparent clouds to emit or to attract them, because the constituent parts of these aero-aqueous regions may possess an abundance or deficiency of electric matter and yet be in perfect reciprocal solution. And lastly their apparent train of light is probably owing only to a continuance of their impression on the eye; as when a fire-stick is whirled in the dark it gives the appearance of a compleat circle of fire: for these white trains of shooting stars quickly vanish, and do not seem to set any thing on fire in their passage, as seems to happen in the transit of fire-balls.

3. The second region or stratum of air terminates I suppose where the twilight ceases to be refracted, that is, where the air is 3000 times rarer than at the surface of the earth; and where it seems probable that the common air ends, and is surrounded by an atmosphere of inflammable gas tenfold rarer than itself. In this region I believe fire-balls sometimes to pass, and at other times the northern lights to exist. One of these fire-balls or draco volans, was observed by Dr. Pringle and many others on Nov. 26, 1758, which was afterwards estimated to have been a mile and a half in circumference, to have been about one hundred miles high, and to have moved towards the north with a velocity of near thirty miles in a second of time. This meteor had a real tail many miles long, which threw off sparks in its course, and the whole exploded with a sound like distant thunder. Philos. Trans. Vol. LI.

Dr. Blagden has related the history of another large meteor, or fire- ball, which was seen the 18th of August, 1783, with many ingenious observations and conjectures. This was estimated to be between 60 and 70 miles high, and to travel 1000 miles at the rate of about twenty miles in a second. This fire-ball had likewise a real train of light left behind it in its passage, which varied in colour; and in some part of its course gave off sparks or explosions where it had been brightest; and a dusky red streak remained visible perhaps a minute. Philos. Trans. Vol. LXXIV.

These fire-balls differ from lightning, and from shooting stars in many remarkable circumstances; as their very great bulk, being a mile and a half in diameter; their travelling 1000 miles nearly horizontally; their throwing off sparks in their passage; and changing colours from bright blue to dusky red; and leaving a train of fire behind them, continuing about a minute. They differ from the northern lights in not being diffused, but passing from one point of the heavens to another in a defined line; and this in a region above the crepuscular atmosphere, where the air is 3000 tines rarer than at the surface of the earth. There has not yet been even a conjecture which can account for these appearances!--One I shall therefore hazard; which, if it does not inform, may amuse the reader.

In the note on l. 123, it was shewn that there is probably a supernatant stratum of inflammable gas or hydrogene, over the common atmosphere; and whose density at the surface where they meet, must be at least ten times less than that upon which it swims; like chemical ether floating upon water, and perhaps without any real contact. 1. In this region, where the aerial atmosphere terminates and the inflammable one begins, the quantity of tenacity or resistance must be almost inconceivable; in which a ball of electricity might pass 1000 miles with greater ease than through a thousandth part of an inch of glass. 2. Such a ball of electricity passing between inflammable and common air would set fire to them in a line as it patted along; which would differ in colour according to the greater proportionate commixture of the two airs; and from the same cause there might occur greater degrees of inflammation, or branches of fire, in some parts of its course.

As these fire-balls travel in a defined line, it is pretty evident from the known laws of electricity, that they must be attracted; and as they are a mile or more in diameter, they must be emitted from a large surface of electric matter; because large nobs give larger sparks, less diffused, and more brightly luminous, than less ones or points, and resist more forceably the emission of the electric matter. What is there in nature can attract them at so great a distance as 1000 miles, and so forceably as to detach an electric spark of a mile diameter? Can volcanos at the time of their eruptions have this effect, as they are generally attended with lightning? Future observations must discover these secret operations of nature! As a stream of common air is carried along with the passage of electric aura from one body to another; it is easy to conceive, that the common air and the inflammable air between which the fire-ball is supposed to pass, will be partially intermixed by being thus agitated, and so far as it becomes intermixed it will take fire, and produce the linear flame and branching sparks above described. In this circumstance of their being attracted, and thence passing in a defined line, the fire-balls seem to differ from the coruscations of the aurora borealis, or northern lights, which probably take place in the same region of the atmosphere; where the common air exists in extreme tenuity, and is covered by a still rarer sphere of inflammable gas, ten times lighter than itself.

As the electric streams, which constitute these northern lights, seem to be repelled or radiated from an accumulation of that fluid in the north, and not attracted like the fireballs; this accounts for the diffusion of their light, as well as the silence of their passage; while their variety of colours, and the permanency of them, and even the breadth of them in different places, may depend on their setting on fire the mixture of inflammable and common air through which they pass; as seems to happen in the transit of the fire-balls.

It was observed by Dr. Priestley that the electric shock taken through inflammable air was red, in common air it is blueish; to these circumstances perhaps some of the colours of the northern lights may bear analogy; though the density of the medium through which light is seen must principally vary its colour, as is well explained by Mr. Morgan. Phil. Trans. Vol. LXXV. Hence lightning is red when seen through a dark cloud, or near the horizon; because the more refrangible rays cannot permeate so dense a medium. But the shooting stars consist of white light, as they are generally seen on clear nights, and nearly vertical: in other situations their light is probably too faint to come to us. But as in some remarkable appearances of the northern lights, as in March, 1716, all the prismatic colours were seen quickly to succeed each other, these appear to have been owing to real combustion; as the density of the interposed medium could not be supposed to change so frequently; and therefore these colours must have been owing to different degrees of heat according to Mr. Morgan's theory of combustion. In Smith's Optics, p. 69. the prismatic colours, and optical deceptions of the northern lights are described by Mr. Cotes.

The Torricellian vacuum, if perfectly free from air, is said by Mr. Morgan and others to be a perfect non-conductor. This circumstance therefore would preclude the electric streams from rising above the atmosphere. But as Mr. Morgan did not try to pass an electric shock through a vacuum, and as air, or something containing air, surrounding the transit of electricity may be necessary to the production of light, the conclusion may perhaps still be dubious. If however the streams of the northern lights were supposed to rise above our atmosphere, they would only be visible at each extremity of their course; where they emerge from, or are again immerged into the atmosphere; but not in their journey through the vacuum; for the absence of electric light in a vacuum is sufficiently proved by the common experiment of shaking a barometer in the dark; the electricity, produced by the friction of the mercury in the glass at its top, is luminous if the barometer has a little air in it; but there is no light if the vacuum be complete.

The aurora borealis, or northern dawn, is very ingeniously accounted for by Dr. Franklin on principles of electricity. He premises the following electric phenomena: 1. that all new fallen snow has much positive electricity standing on its surface. 2. That about twelve degrees of latitude round the poles are covered with a crust of eternal ice, which is impervious to the electric fluid. 3. That the dense part of the atmosphere rises but a few miles high; and that in the rarer parts of it the electric fluid will pass to almost any distance.

Hence he supposes there must be a great accumulation of positive electric matter on the fresh fallen snow in the polar regions; which, not being able to pass through the crust of ice into the earth, must rise into the rare air of the upper parts of our atmosphere, which will the least resist its passage; and passing towards the equator descend again into the denser atmosphere, and thence into the earth in silent streams. And that many of the appearances attending these lights are optical deceptions, owing to the situation of the eye that beholds them; which makes all ascending parallel lines appear to converge to a point.

The idea, above explained in note on l. 123, of the existence of a sphere of inflammable gas over the aerial atmosphere would much favour this theory of Dr. Franklin; because in that case the dense aerial atmosphere would rise a much less height in the polar regions, diminishing almost to nothing at the pole itself; and thus give an easier passage to the ascent of the electric fluid. And from the great difference in the specific gravity of the two airs, and the velocity of the earth's rotation, there must be a place between the poles and the equator, where the superior atmosphere of inflammable gas would terminate; which would account for these streams of the aurora borealis not appearing near the equator; add to this that it is probable the electric fluid may be heavier than the magnetic one; and will thence by the rotation of the earth's surface ascend over the magnetic one by its centrifugal force; and may thus be induced to rise through the thin stratum of aerial atmosphere over the poles. See note on Canto II. l. 193. I shall have occasion again to mention this great accumulation of inflammable air over the poles; and to conjecture that these northern lights may be produced by the union of inflammable with common air, without the assistance of the electric spark to throw them into combustion.

The antiquity of the appearance of northern lights has been doubted; as none were recorded in our annals since the remarkable one on Nov. 14, 1574, till another remarkable one on March 6, 1716, and the three following nights, which were seen at the same time in Ireland, Russia, and Poland, extending near 30 degrees of longitude and from about the 50th degree of latitude over almost all the north of Europe. There is however reason to believe them of remote antiquity though inaccurately described; thus the following curious passage from the Book of Maccabees, (B. II. c. v.) is such a description of them, as might probably be given by an ignorant and alarmed people. "Through all the city, for the space of almost forty days, there were seen horsemen running in the air, in cloth of gold, and armed with lances, like a band of soldiers; and troops of horsemen in array encountering and running one against another, with shaking of shields and multitude of pikes, and drawing of swords, and casting of darts, and glittering of golden ornaments and harness."

NOTE II.--PRIMARY COLOURS.

_Cling round the aerial bow with prisms bright, And pleased untwist the sevenfold threads of light._

CANTO I. l. 117.

The manner in which the rainbow is produced was in some measure understood before Sir Isaac Newton had discovered his theory of colours. The first person who expressly shewed the rainbow to be formed by the reflection of the sunbeams from drops of falling rain was Antonio de Dominis. This was afterwards more fully and distinctly explained by Des Cartes. But what caused the diversity of its colours was not then understood; it was reserved for the immortal Newton to discover that the rays of light consisted of seven combined colours of different refrangibility, which could be seperated at pleasure by a wedge of glass. Pemberton's View of Newton.

Sir Isaac Newton discovered that the prismatic spectrum was composed of seven colours in the following proportions, violet 80, indigo 40, blue 60, green 60, yellow 48, orange 27, red 45. If all these colours be painted on a circular card in the proportions above mentioned, and the card be rapidly whirled on its center, they produce in the eye the sensation of white. And any one of these colours may be imitated by painting a card with the two colours which are contiguous to it, in the same proportions as in the spectrum, and whirling them in the same manner. My ingenious friend, Mr. Galton of Birmingham, ascertained in this manner by a set of experiments the following propositions; the truth of which he had preconceived from the above data.

1. Any colour in the prismatic spectrum may be imitated by a mixture of the two colours contiguous to it.

2. If any three successive colours in the prismatic spectrum are mixed, they compose only the second or middlemost colour.

3. If any four succesive colours in the prismatic spectrum be mixed, a tint similar to a mixture of the second and third colours will be produced, but not precisely the same, because they are not in the same proportion.

4. If beginning with any colour in the circular spectrum, you take of the second colour a quantity equal to the first, second, and third; and add to that the fifth colour, equal in quantity to the fourth, fifth, and sixth; and with these combine the seventh colour in the proportion it exists in the spectrum, white will be produced. Because the first, second, and third, compose only the second; and the fourth, fifth, and sixth, compose only the fifth; therefore if the seventh be added, the same effect is produced, as if all the seven were employed.

5. Beginning with any colour in the circular spectrum, if you take a tint composed of a certain proportion of the second and third, (equal in quantity to the first, second, third, and fourth,) and add to this the sixth colour equal in quantity to the fifth, sixth, and seventh, white will be produced.

From these curious experiments of Mr. Galton many phenomena in the chemical changes of colours may probably become better understood; especially if, as I suppose, the same theory must apply to transmitted colours, as to reflected ones. Thus it is well known, that if the glass of mangonese, which is a tint probably composed of violet and indigo, be mixed in a certain proportion with the glass of lead, which is yellow; that the mixture becomes transparent. Now from Mr. Galton's experiments it appears, that in reflected colours such a mixture would produce white, that is, the same as if all the colours were reflected. And therefore in transmitted colours the same circumstances must produce transparency, that is, the same as if all the colours were transmitted. For the particles, which constitute the glass of mangonese will transmit red, violet, indigo, and blue; and those of the glass of lead will transmit orange, yellow, and green; hence all the primary colours by a mixture of these glasses become transmitted, that is, the glass becomes transparent.

Mr. Galton has further observed that five successive prismatic colours may be combined in such proportions as to produce but one colour, a circumstance which might be of consequence in the art of painting. For if you begin at any part of the circular spectrum above described, and take the first, second, and third colours in the proportions in which they exist in the spectrum; these will compose only the second colour equal in quantity to the first, second, and third; add to these the third, fourth, and fifth in the proportion they exist in the spectrum, and these will produce the fourth colour equal in quantity to the third, fourth, and fifth. Consequently this is precisely the same thing, as mixing the second and fourth colours only; which mixture would only produce the third colour. Therefore if you combine the first, second, fourth, and fifth in the proportions in which they exist in the spectrum, with double the quantity of the third colour, this third colour will be produced. It is probable that many of the unexpected changes in mixing colours on a painter's easle, as well as in more fluid chemical mixtures, may depend on these principles rather than on a new arrangement or combination of their minute particles.

Mr. Galton further observes, that white may universally be produced by the combination of one prismatic colour, and a tint intermediate to two others. Which tint may be distinguished by a name compounded of the two colours, to which it is intermediate. Thus white is produced by a mixture of red with blue-green. Of orange with indigo-blue. Of Yellow with violet-indigo. Of green with red-violet. Of blue with Orange-red. Of indigo with yellow-orange. Of violet with green-yellow. Which he further remarks exactly coincides with the theory and facts mentioned by Dr. Robert Darwin of Shrewsbury in his account of ocular spectra; who has shewn that when one of these contrasted colours has been long viewed, a spectrum or appearance of the other becomes visible in the fatigued eye. Philos. Trans. Vol. LXXVI. for the year 1786.

These experiments of Mr. Galton might much assist the copper-plate printers of callicoes and papers in colours; as three colours or more might be produced by two copper-plates. Thus suppose some yellow figures were put on by the first plate, and upon some parts of these yellow figures and on other parts of the ground blue was laid on by another copper-plate. The three colours of yellow, blue, and green might be produced; as green leaves with yellow and blue flowers.

NOTE III.--COLOURED CLOUDS.

_Eve's silken couch with gorgeous tints adorn, Or fire the arrowy throne of rising morn._

CANTO I. l. 119.

The rays from the rising and setting sun are refracted by our spherical atmosphere, hence the most refrangible rays, as the violet, indigo, and blue are reflected in greater quantities from the morning and evening skies; and the least refrangible ones, as red and orange, are last seen about the setting sun. Hence Mr. Beguelin observed that the shadow of his finger on his pocket-book was much bluer in the morning and evening, when the shadow was about eight times as long as the body from which it was projected. Mr. Melville observes, that the blue rays being more refrangible are bent down in the evenings by our atmosphere, while the red and orange being less refrangible continue to pass on and tinge the morning and evening clouds with their colours. See Priestley's History of Light and Colours, p. 440. But as the particles of air, like those of water, are themselves blue, a blue shadow may be seen at all times of the day, though much more beautifully in the mornings and evenings, or by means of a candle in the middle of the day. For if a shadow on a piece of white paper is produced by placing your finger between the paper and a candle in the day light, the shadow will appear very blue; the yellow light of the candle upon the other parts of the paper apparently deepens the blue by its contrast; these colours being opposite to each other, as explained in note II.

Colours are produced from clouds or mists by refraction, as well as by reflection. In riding in the night over an unequal country I observed a very beautiful coloured halo round the moon, whenever I was covered with a few feet of mist, as I ascended from the vallies; which ceased to appear when I rose above the mist. This I suppose was owing to the thinness of the stratum of mist, in which I was immersed; had it been thicker, the colours refracted by the small drops, of which a fog consists, would not have passed through it down to my eye.

There is a bright spot seen on the cornea of the eye, when we face a window, which is much attended to by portrait painters; this is the light reflected from the spherical surface of the polished cornea, and brought to a focus; if the observer is placed in this focus, he sees the image of the window; if he is placed before or behind the focus, he only sees a luminous spot, which is more luminous and of less extent, the nearer he approaches to the focus. The luminous appearance of the eyes of animals in the dusky corners of a room, or in holes in the earth, may arise in some instances from the same principle; viz. the reflection of the light from the spherical cornea; which will be coloured red or blue in some degree by the morning, evening, or meridian light; or by the objects from which that light is previously reflected. In the cavern at Colebrook Dale, where the mineral tar exsudes, the eyes of the horse, which was drawing a cart from within towards the mouth of it, appeared like two balls of phosphorus, when he was above 100 yards off, and for a long time before any other part of the animal was visible. In this case I suspect the luminous appearance to have been owing to the light, which had entered the eye, being reflected from the back surface of the vitreous humour, and thence emerging again in parallel rays from the animals eye, as it does from the back surface of the drops of the rainbow, and from the water-drops which lie, perhaps without contact, on cabbage-leaves, and have the brilliancy of quicksilver. This accounts for this luminous appearance being best seen in those animals which have large apertures in their iris, as in cats and horses, and is the only part visible in obscure places, because this is a better reflecting surface than any other part of the animal. If any of these emergent rays from the animals eye can be supposed to have been reflected from the choroid coat through the semi-transparent retina, this would account for the coloured glare of the eyes of dogs or cats and rabits in dark corners.

NOTE IV.--COMETS.

_Alarm with comet-blaze the sapphire plain, The wan stars glimmering through its silver train._

CANTO I. l. 133.

There have been many theories invented to account for the tails of comets. Sir Isaac Newton thinks that they consist of rare vapours raised from the nucleus of the comet, and so rarefied by the sun's heat as to have their general gravitation diminished, and that they in consequence ascend opposite to the sun, and from thence reflect the rays of light. Dr. Halley compares the light of the tails of comets to the streams of the aurora borealis, and other electric effluvia. Philos. Trans. No. 347.

Dr. Hamilton observes that the light of small stars are seen undiminished through both the light of the tails of comets, and of the aurora borealis, and has further illustrated their electric analogy, and adds that the tails of comets consist of a lucid self-shining substance which has not the power of refracting or reflecting the rays of light. Essays.

The tail of the comet of 1744 at one time appeared to extend above 16 degrees from its body, and must have thence been above twenty three millions of miles long. And the comet of 1680, according to the calculations of Dr. Halley on November the 11th, was not above one semi- diameter of the earth, or less than 4000 miles to the northward of the way of the earth; at which time had the earth been in that part of its orbit, what might have been the consequence! no one would probably have survived to have registered the tremendous effects.

The comet of 1531, 1607, and 1682 having returned in the year 1759, according to Dr. Halley's prediction in the Philos. Trans. for 1705, there seems no reason to doubt that all the other comets will return after their proper periods. Astronomers have in general acquiesced in the conjecture of Dr. Halley, that the comets of 1532, and 1661 are one and the same comet, from the similarity of the elements of their orbits, and were therefore induced to expect its return to its perihelium 1789. As this comet is liable to be disturbed in its ascent from the sun by the planets Jupiter and Saturn, Dr. Maskelyne expected its return to its perihelium in the beginning of the year 1789, or the latter end of the year 1788, and certainly sometime before the 27th of April, 1789, which prediction has not been fulfilled. Phil. Trans. Vol. LXXVI.

NOTE V.--SUN'S RAYS.

_Or give the sun's phlogistic orb to roll._

CANTO I. l. 136.

The dispute among philosophers about phlogiston is not concerning the existence of an inflammable principle, but rather whether there be one or more inflammable principles. The disciples of Stahl, which till lately included the whole chemical world, believed in the identity of phlogiston in all bodies which would flame or calcine. The disciples of Lavoisier pay homage to a plurality of phlogistons under the various names of charcoal, sulphur, metals, &c. Whatever will unite with _pure_ air, and thence compose an acid, is esteemed in this ingenious theory to be a different kind of phlogistic or inflammable body. At the same time there remains a doubt whether these inflammable bodies, as metals, sulphur, charcoal, &c. may not be compounded of the same phlogiston along with some other material yet undiscovered, and thus an unity of phlogiston exist, as in the theory of Stahl, though very differently applied in the explication of chemical phenomena.

Some modern philosophers are of opinion that the sun is the great fountain from which the earth and other planets derive all the phlogiston which they possess; and that this is formed by the combination of the solar rays with all opake bodies, but particularly with the leaves of vegetables, which they suppose to be organs adapted to absorb them. And that as animals receive their nourishment from vegetables they also obtain in a secondary manner their phlogiston from the sun. And lastly as great masses of the mineral kingdom, which have been found in the thin crust of the earth which human labour has penetrated, have evidently been formed from the recrements of animal and vegetable bodies, these also are supposed thus to have derived their phlogiston from the sun.

Another opinion concerning the sun's rays is, that they are not luminous till they arrive at our atmosphere; and that there uniting with some part of the air they produce combustion, and light is emitted, and that an etherial acid, yet undiscovered, is formed from this combustion.

The more probable opinion is perhaps, that the sun is a phlogistic mass of matter, whose surface is in a state of combustion, which like other burning bodies emits light with immense velocity in all directions; that these rays of light act upon all opake bodies, and combining with them either displace or produce their elementary heat, and become chemically combined with the phlogistic part of them; for light is given out when phlogistic bodies unite with the oxygenous principle of the air, as in combustion, or in the reduction of metallic calxes; thus in presenting to the flame of a candle a letter-wafer, (if it be coloured with red- lead,) at the time the red-lead becomes a metallic drop, a flash of light is perceived. Dr. Alexander Wilson very ingeniously endeavours to prove that the sun is only in a state of combustion on its surface, and that the dark spots seen on the disk are excavations or caverns through the luminous crust, some of which are 4000 miles in diameter. Phil. Trans. 1774. Of this I shall have occasion to speak again.

NOTE VI.--CENTRAL FIRES.

_Round her still centre tread the burning soil, And watch the billowy Lavas, as they boil._

CANTO I. l. 139.

M. de Mairan in a paper published in the Histoire de l'Academie de Sciences, 1765, has endeavoured to shew that the earth receives but a small part of the heat which it possesses, from the sun's rays, but is principally heated by fires within itself. He thinks the sun is the cause of the vicissitudes of our seasons of summer and winter by a very small quantity of heat in addition to that already residing in the earth, which by emanations from the centre to the circumference renders the surface habitable, and without which, though the sun was constantly to illuminate two thirds of the globe at once, with a heat equal to that at the equator, it would soon become a mass of solid ice. His reasonings and calculations on this subject are too long and too intricate to be inserted here, but are equally curious and ingenious and carry much conviction along with them.

The opinion that the center of the earth consists of a large mass of burning lava, has been espoused by Boyle, Boerhave, and many other philosophers. Some of whom considering its supposed effects on vegetation and the formation of minerals have called it a second sun. There are many arguments in support of this opinion, 1. Because the power of the sun does not extend much beyond ten feet deep into the earth, all below being in winter and summer always of the same degree of heat, viz. 48, which being much warmer than the mildest frost, is supposed to be sustained by some internal distant fire. Add to this however that from experiments made some years ago by Dr. Franklin the spring-water at Philadelphia appeared to be of 52 deg. of heat, which seems further to confirm this opinion, since the climates in North America are supposed to be colder than those of Europe under similar degrees of latitude. 2. Mr. De Luc in going 1359 feet perpendicular into the mines of Hartz on July the 5th, 1778, on a very fine day found the air at the bottom a little warmer than at the top of the shaft. Phil. Trans. Vol. LXIX. p. 488. In the mines in Hungary, which are 500 cubits deep, the heat becomes very troublesome when the miners get below 480 feet depth. _Morinus de Locis subter_. p. 131. But as some other deep mines as mentioned by Mr. Kirwan are said to possess but the common heat of the earth; and as the crust of the globe thus penetrated by human labour is so thin compared with the whole, no certain deduction can be made from these facts on either side of the question. 3. The warm-springs in many parts of the earth at great distance from any Volcanos seem to originate from the condensation of vapours arising from water which is boiled by subterraneous fires, and cooled again in their passage through a certain length of the colder soil; for the theory of chemical solution will not explain the equality of their heat at all seasons and through so many centuries. See note on Fucus in Vol. II. See a letter on this subject in Mr. Pilkinton's View of Derbyshire from Dr. Darwin. 4. From the situations of volcanos which are always found upon the summit of the highest mountains. For as these mountains have been lifted up and lose several of their uppermost strata as they rise, the lowest strata of the earth yet known appear at the tops of the highest hills; and the beds of the Volcanos upon these hills must in consequence belong to the lowest strata of the earth, consisting perhaps of granite or basaltes, which were produced before the existance of animal or vegetable bodies, and might constitute the original nucleus of the earth, which I have supposed to have been projected from the sun, hence the volcanos themselves appear to be spiracula or chimneys belonging to great central fires. It is probably owing to the escape of the elastic vapours from these spiracula that the modern earthquakes are of such small extent compared with those of remote antiquity, of which the vestiges remain all over the globe. 5. The great size and height of the continents, and the great size and depth of the South-sea, Atlantic, and other oceans, evince that the first earthquakes, which produced these immense changes in the globe, must have been occasioned by central fires. 6. The very distant and expeditious communication of the shocks of some great earthquakes. The earthquake at Lisbon in 1755 was perceived in Scotland, in the Peak of Derbyshire, and in many other distant parts of Europe. The percussions of it travelled with about the velocity of sound, viz. about thirteen miles in a minute. The earthquake in 1693 extended 2600 leagues. (Goldsmith's History.) These phenomena are easily explained if the central parts of the earth consist of a fluid lava, as a percussion on one part of such a fluid mass would be felt on other parts of its confining vault, like a stroke on a fluid contained in a bladder, which however gentle on one side is perceptible to the hand placed on the other; and the velocity with which such a concussion would travel would be that of sound, or thirteen miles in a minute. For further information on this part of the subject the reader is referred to Mr. Michell's excellent Treatise on Earthquakes in the Philos. Trans. Vol. LI. 7. That there is a cavity at the center of the earth is made probable by the late experiments on the attraction of mountains by Mr. Maskerlyne, who supposed from other considerations that the density of the earth near the surface should be five times less than its mean density. Phil. Trans. Vol. LXV. p. 498. But found from the attraction of the mountain Schehallien, that it is probable, the mean density of the earth is but double that of the hill. Ibid. p. 532. Hence if the first supposition be well founded there would appear to be a cavity at the centre of considerable magnitude, from whence the immense beds and mountains of lava, toadstone, basaltes, granite, &c. have been protruded. 8. The variation of the compass can only be accounted for by supposing the central parts of the earth to consist of a fluid mass, and that part of this fluid is iron, which requiring a greater degree of heat to bring it into fusion than glass or other metals, remains a solid, and the vis inertiae of this fluid mass with the iron in it, occasions it to perform fewer revolutions than the crust of solid earth over it, and thus it is gradually left behind, and the place where the floating iron resides is pointed to by the direct or retrograde motions of the magnetic needle. This seems to have been nearly the opinion of Dr. Halley and Mr. Euler.

NOTE VII.--ELEMENTARY HEAT.

_Or sphere on sphere in widening waves expand, And glad with genial warmth the incumbent land._

CANTO I. l. 143.

A certain quantity of heat seems to be combined with all bodies besides the sensible quantity which gravitates like the electric fluid amongst them. This combined heat or latent heat of Dr. Black, when set at liberty by fermentation, inflammation, crystallization, freezing, or other chemical attractions producing new _combinations_, passes as a fluid element into the surrounding bodies. And by thawing, diffusion of neutral salts in water, melting, and other chemical _solutions_, a portion of heat is attracted from the bodies in vicinity and enters into or becomes combined with the new solutions.

Hence a _combination_ of metals with acids, of essential oils and acids, of alcohol and water, of acids and water, give out heat; whilst a _solution_ of snow in water or in acids, and of neutral salts in water, attract heat from the surrounding bodies. So the acid of nitre mixed with oil of cloves unites with it and produces a most violent flame; the same acid of nitre poured on snow instantly dissolves it and produces the greatest degree of cold yet known, by which at Petersburgh quicksilver was first frozen in 1760.

Water may be cooled below 32 deg. without being frozen, if it be placed on a solid floor and secured from agitation, but when thus cooled below the freezing point the least agitation turns part of it suddenly into ice, and when this sudden freezing takes place a thermometer placed in it instantly rises as some heat is given out in the act of congelation, and the ice is thus left with the same _sensible_ degree of cold as the water had possessed before it was agitated, but is nevertheless now combined with less _latent_ heat.

A cubic inch of water thus cooled down to 32 deg. mixed with an equal quantity of boiling water at 212 deg. will cool it to the middle number between these two, or to 122. But a cubic inch of ice whose sensible cold also is but 32, mixed with an equal quantity of boiling water, will cool it six times as much as the cubic inch of cold water above-mentioned, as the ice not only gains its share of the sensible or gravitating heat of the boiling water but attracts to itself also and combines with the quantity of latent heat which it had lost at the time of its congelation.

So boiling water will acquire but 212 deg. of heat under the common pressure of the atmosphere, but the steam raised from it by its expansion or by its solution in the atmosphere combines with and carries away a prodigious quantity of heat which it again parts with on its condensation; as is seen in common distillation where the large quantity of water in the worm-tub is so soon heated. Hence the evaporation of ether on a thermometer soon sinks the mercury below freezing, and hence a warmth of the air in winter frequently succeeds a shower.

When the matter of heat or calorique is set at liberty from its combinations, as by inflammation, it passes into the surrounding bodies, which possess different capacities of acquiring their share of the loose or sensible heat; thus a pint measure of cold water at 48 deg. mixed with a pint of boiling water at 212 deg. will cool it to the degree between these two numbers, or to 154 deg., but it requires two pint measures of quicksilver at 48 deg. of heat to cool one pint of water as above. These and other curious experiments are adduced by Dr. Black to evince the existance of combined or latent heat in bodies, as has been explained by some of his pupils, and well illustrated by Dr. Crawford. The world has long been in expectation of an account of his discoveries on this subject by the celebrated author himself.

As this doctrine of elementary heat in its fluid and combined state is not yet universally received, I shall here add two arguments in support of it drawn from different sources, viz. from the heat given out or absorbed by the mechanical condensation or expansion of the air, and perhaps of other bodies, and from the analogy of the various phenomena of heat with those of electricity.

I. If a thermometer be placed in the receiver of an air-pump, and the air hastily exhausted, the thermometer will sink some degrees, and the glass become steamy; the same occurs in hastily admitting a part of the air again. This I suppose to be produced by the expansion of part of the air, both during the exhaustion and re-admission of it; and that the air so expanded becomes capable of attracting from the bodies in its vicinity a part of their heat, hence the vapours contained in it and the glass receiver are for a time colder and the steam is precipitated. That the air thus parts with its moisture from the cold occasioned by its rarefaction and not simply by the rarefaction itself is evident, because in a minute or two the same rarefied air will again take up the dew deposited on the receiver; and because water will evaporate sooner in rare than in dense air.

There is a curious phenomenon similar to this observed in the fountain of Hiero constructed on a large scale at the Chemnicensian mines in Hungary. In this machine the air in a large vessel is compressed by a column of water 260 feet high, a stop-cock is then opened, and as the air issues out with great vehemence, and thus becomes immediately greatly expanded, so much cold is produced that the moisture from this stream of air is precipitated in the form of snow, and ice is formed adhering to the nosel of the cock. This remarkable circumstance is described at large with a plate of the machine in Philos. Trans. Vol. LII. for 1761.

The following experiment is related by Dr. Darwin in the Philos. Trans. Vol. LXXVIII. Having charged an air-gun as forcibly as he well could the air-cell and syringe became exceedingly hot, much more so than could be ascribed to the friction in working it; it was then left about half an hour to cool down to the temperature of the air, and a thermometer having been previously fixed against a wall, the air was discharged in a continual stream on its bulb, and it sunk many degrees. From these three experiments of the steam in the exhausted receiver being deposited and re-absorbed, when a part of the air is exhausted or re-admitted, and the snow produced by the fountain of Hiero, and the extraordinary heat given out in charging, and the cold produced in discharging an air-gun, there is reason to conclude that when air is mechanically compressed the elementary fluid heat is pressed out of it, and that when it is mechanically expanded the same fluid heat is re-absorbed from the common mass.

It is probable all other bodies as well as air attract heat from their neighbours when they are mechanically expanded, and give it out when they are mechanically condensed. Thus when a vibration of the particles of hard bodies is excited by friction or by percussion, these particles mutually recede from and approach each other reciprocally; at the times of their recession from each other, the body becomes enlarged in bulk, and is then in a condition to attract heat from those in its vicinity with great and sudden power; at the times of their approach to each other this heat is again given out, but the bodies in contact having in the mean while received the heat they had thus lost, from other bodies behind them, do not so suddenly or so forcibly re-absorb the heat again from the body in vibration; hence it remains on its surface like the electric fluid on a rubbed glass globe, and for the same reason, because there is no good conductor to take it up again. Hence at every vibration more and more heat is acquired and stands loose upon the surface; as in filing metals or rubbing glass tubes; and thus a smith with a few strokes on a nail on his anvil can make it hot enough to light a brimstone-match; and hence in striking flint and steel together heat enough is produced to vitrify the parts thus strucken off, the quantity of which heat is again probably increased by the new chemical combination.

II. The analogy between the phenomena of the electric fluid and of heat furnishes another argument in support of the existence of heat as a gravitating fluid. 1. They are both accumulated by friction on the excited body. 2. They are propagated easily or with difficalty along the same classes of bodies; with ease by metals, with less ease by water; and with difficulty by resins, bees-wax, silk, air, and glass. Thus glass canes or canes of sealing-wax may be melted by a blow-pipe or a candle within a quarter of an inch of the fingers which hold them, without any inconvenient heat, while a pin or other metallic substance applyed to the flame of a candle so readily conducts the heat as immediately to burn the fingers. Hence clothes of silk keep the body warmer than clothes of linen of equal thickness, by confining the heat upon the body. And hence plains are so much warmer than the summits of mountains by the greater density of the air confining the acquired heat upon them. 3. They both give out light in their passage through air, perhaps not in their passage through a vacuum. 4. They both of them fuse or vitrify metals. 5. Bodies after being electrized if they are mechanically extended will receive a greater quantity of electricity, as in Dr. Franklin's experiment of the chain in the tankard; the same seems true in respect to heat as explained above. 6. Both heat and electricity contribute to suspend steam in the atmosphere by producing or increasing the repulsion of its particles. 7. They both gravitate, when they have been accumulated, till they find their equilibrium.

If we add to the above the many chemical experiments which receive an easy and elegant explanation from the supposed matter of heat, as employed in the works of Bergman and Lavoisier, I think we may reasonably allow of its existence as an element, occasionally combined with other bodies, and occasionally existing as a fluid, like the electric fluid gravitating amongst them, and that hence it may be propagated from the central fires of the earth to the whole mass, and contribute to preserve the mean heat of the earth, which in this country is about 48 degrees but variable from the greater or less effect of the sun's heat in different climates, so well explained in Mr. Kirwan's Treatise on the Temperature of different Latitudes. 1787, Elmsly. London.

NOTE VIII.--MEMNON'S LYRE.

_So to the sacred Sun in Memnon's fane Spontaneous concords quired the matin strain._

CANTO I. l. 183.

The gigantic statue of Memnon in his temple at Thebes had a lyre in his hands, which many credible writers assure us, sounded when the rising sun shone upon it. Some philosophers have supposed that the sun's light possesses a mechanical impulse, and that the sounds abovementioned might be thence produced. Mr. Michell constructed a very tender horizontal balance, as related by Dr. Priestley in his history of light and colours, for this purpose, but some experiments with this balance which I saw made by the late Dr. Powel, who threw the focus of a large reflector on one extremity of it, were not conclusive either way, as the copper leaf of the balance approached in one experiment and receded in another.

There are however methods by which either a rotative or alternating motion may be produced by very moderate degrees of heat. If a straight glass tube, such as are used for barometers, be suspended horizontally before a fire, like a roasting spit, it will revolve by intervals; for as glass is a bad conductor of heat the side next the fire becomes heated sooner than the opposite side, and the tube becomes bent into a bow with the external part of the curve towards the fire, this curve then falls down and produces a fourth part of a revolution of the glass tube, which thus revolves with intermediate pauses.

Another alternating motion I have seen produced by suspending a glass tube about eight inches long with bulbs at each end on a centre like a scale beam. This curious machine is filled about one third part with purest spirit of wine, the other two thirds being a vacuum, and is called a pulse-glass, if it be placed in a box before the fire, so that either bulb, as it rises, may become shaded from the fire, and exposed to it when it descends, an alternate libration of it is produced. For spirit of wine in vacuo emits steam by a very small degree of heat, and this steam forces the spirit beneath it up into the upper bulb, which therefore descends. It is probable such a machine on a larger scale might be of use to open the doors or windows of hot-houses or mellon- frames, when the air within them should become too much heated, or might be employed in more important mechanical purposes.

On travelling through a hot summer's day in a chaise with a box covered with leather on the fore-axle-tree, I observed, as the sun shone upon the black leather, the box began to open its lid, which at noon rose above a foot, and could not without great force be pressed down; and which gradually closed again as the sun declined in the evening. This I suppose might with still greater facility be applied to the purpose of opening melon-frames or the sashes of hot-houses.

The statue of Memnon was overthrown and sawed in two by Cambyses to discover its internal structure, and is said still to exist. See Savary's Letters on Egypt. The truncated statue is said for many centuries to have saluted the rising sun with chearful tones, and the setting sun with melancholy ones.

NOTE IX.--LUMINOUS INSECTS.

_Star of the earth, and diamond of the night._

CANTO I. l. 196.

There are eighteen species of Lampyris or glow-worm, according to Linneus, some of which are found in almost every part of the world. In many of the species the females have no wings, and are supposed to be discovered by the winged males by their shining in the night. They become much more lucid when they put themselves in motion, which would seem to indicate that their light is owing to their respiration; in which process it is probable phosphoric acid is produced by the combination of vital air with some part of the blood, and that light is given out through their transparent bodies by this slow internal combustion.

There is a fire-fly of the beetle-kind described in the Dict. Raisonne under the name of Acudia, which is said to be two inches long, and inhabits the West-Indies and South America; the natives use them instead of candles, putting from one to three of them under a glass. Madam Merian says, that at Surinam the light of this fly is so great, that she saw sufficiently well by one of them to paint and finish one of the figures of them in her work on insects. The largest and oldest of them are said to become four inches long, and to shine like a shooting star as they fly, and are thence called Lantern-bearers. The use of this light to the insect itself seems to be that it may not fly against objects in the night; by which contrivance these insects are enabled to procure their sustenance either by night or day, as their wants may require, or their numerous enemies permit them; whereas some of our beetles have eyes adapted only to the night, and if they happen to come abroad too soon in the evening are so dazzled that they fly against every thing in their way. See note on Phosphorus, No. X.

In some seas, as particularly about the coast of Malabar, as a ship floats along, it seems during the night to be surrounded with fire, and to leave a long tract of light behind it. Whenever the sea is gently agitated it seems converted into little stars, every drop as it breaks emits light, like bodies electrified in the dark. Mr. Bomare says, that when he was at the port of Cettes in Languedoc, and bathing with a companion in the sea after a very hot day, they both appeared covered with fire after every immersion, and that laying his wet hand on the arm of his companion, who had not then dipped himself, the exact mark of his hand and fingers was seen in characters of fire. As numerous microscopic insects are found in this shining water, its light has been generally ascribed to them, though it seems probable that fish-slime in hot countries may become in such a state of incipient putrefaction as to give light, especially when by agitation it is more exposed to the air; otherwise it is not easy to explain why agitation should be necessary to produce this marine light. See note on Phosphorus No. X.

NOTE X.--PHOSPHORUS.

_Or mark in shining letters Kunckel's name In the pale phosphor's self-consuming flame._

CANTO I. l. 231.

Kunckel, a native of Hamburgh, was the first who discovered to the world the process for producing phosphorus; though Brandt and Boyle were likewise said to have previously had the art of making it. It was obtained from sal microcosmicum by evaporation in the form of an acid, but has since been found in other animal substances, as in the ashes of bones, and even in some vegetables, as in wheat flour. Keir's chemical Dict. This phosphoric acid is like all other acids united with vital air, and requires to be treated with charcoal or phlogiston to deprive it of this air, it then becomes a kind of animal sulphur, but of so inflammable a nature, that on the access of air it takes fire spontaneously, and as it burns becomes again united with vital air, and re-assumes its form of phosphoric acid.

As animal respiration seems to be a kind of slow combustion, in which it is probable that phosphoric acid is produced by the union of phosphorus with the vital air, so it is also probable that phosphoric acid is produced in the excretory or respiratory vessels of luminous insects, as the glow-worm and fire-fly, and some marine insects. From the same principle I suppose the light from putrid fish, as from the heads of hadocks, and from putrid veal, and from rotten wood in a certain state of their putrefaction, is produced, and phosphorus thus slowly combined with air is changed into phosphoric acid. The light from the Bolognian stone, and from calcined shells, and from white paper, and linen after having been exposed for a time to the sun's light, seem to produce either the phosphoric or some other kind of acid from the sulphurous or phlogistic matter which they contain. See note on Beccari's shells. l. 180.

There is another process seems similar to this slow combustion, and that is _bleaching_. By the warmth and light of the sun the water sprinkled upon linen or cotton cloth seems to be decomposed, (if we credit the theory of M. Lavoisier,) and a part of the vital air thus set at liberty and uncombined and not being in its elastic form, more easily dissolves the colouring or phlogistic matter of the cloth, and produces a new acid, which is itself colourless, or is washed out of the cloth by water. The new process of bleaching confirms a part of this theory, for by uniting much vital air to marine acid by distilling it from manganese, on dipping the cloth to be bleached in water repleat with this super-aerated marine acid, the colouring matter disappears immediately, sooner indeed in cotton than in linen. See note XXXIV.

There is another process which I suspect bears analogy to these above- mentioned, and that is the rancidity of animal fat, as of bacon; if bacon be hung up in a warm kitchen, with much salt adhering on the outside of it, the fat part of it soon becomes yellow and rancid; if it be washed with much cold water after it has imbibed the salt, and just before it is hung up, I am well informed, that it will not become rancid, or in very slight degrees. In the former case I imagine the salt on the surface of the bacon attracts water during the cold of the night, which is evaporated during the day, and that in this evaporation a part of the water becomes decomposed, as in bleaching, and its vital air uniting with greater facility in its unelastic state with the animal fat, produces an acid, perhaps of the phosphoric kind, which being of a fixed nature lies upon the bacon, giving it the yellow colour and rancid taste. It is remarkable that the super-aerated marine acid does not bleach living animal substances, at least it did not whiten a part of my hand which I for some minutes exposed to it.

NOTE XI.--STEAM-ENGINE.

_Quick moves the balanced beam, of giant-birth, Wields his large limbs, and nodding shakes the earth._

CANTO I. l. 261.

The expansive force of steam was known in some degree to the antients, Hero of Alexandria describes an application of it to produce a rotative motion by the re-action of steam issuing from a sphere mounted upon an axis, through two small tubes bent into tangents, and issuing from the opposite sides of the equatorial diameter of the sphere, the sphere was supplied with steam by a pipe communicating with a pan of boiling water, and entering the sphere at one of its poles.

A french writer about the year 1630 describes a method of raising water to the upper part of a house by filling a chamber with steam, and suffering it to condense of itself, but it seems to have been mere theory, as his method was scarcely practicable as he describes it. In 1655 the Marquis of Worcester mentions a method of raising water by fire in his Century of Inventions, but he seems only to have availed himself of the expansive force and not to have known the advantages arising from condensing the steam by an injection of cold water. This latter and most important improvement seems to have been made by Capt. Savery sometime prior to 1698, for in that year his patent for the use of that invention was confirmed by act of parliament. This gentleman appears to have been the first who reduced the machine to practice and exhibited it in an useful form. This method consisted only in expelling the air from a vessel by steam and condensing the steam by an injection of cold water, which making a vacuum, the pressure of the atmosphere forced the water to ascend into the steam-vessel through a pipe of 24 to 26 feet high, and by the admission of dense steam from the boiler, forcing the water in the steam-vessel to ascend to the height desired. This construction was defective because it required very strong vessels to resist the force of the steam, and because an enormous quantity of steam was condensed by coming in contact with the cold water in the steam-vessel.

About or soon after that time M. Papin attempted a steam-engine on similar principles but rather more defective in its construction.

The next improvement was made very soon afterwards by Messrs. Newcomen and Cawley of Dartmouth, it consisted in employing for the steam-vessel a hollow cylinder, shut at bottom and open at top, furnished with a piston sliding easily up and down in it, and made tight by oakum or hemp, and covered with water. This piston is suspended by chains from one end of a beam, moveable upon an axis in the middle of its length, to the other end of this beam are suspended the pump-rods.

The danger of bursting the vessels was avoided in this machine, as however high the water was to be raised it was not necessary to increase the density of the steam but only to enlarge the diameter of the cylinder.

Another advantage was, that the cylinder not being made so cold as in Savary's method, much less steam was lost in filling it after each condensation.

The machine however still remained imperfect, for the cold water thrown into the cylinder acquired heat from the steam it condensed, and being in a vessel exhausted of air it produced steam itself, which in part resisted the action of the atmosphere on the piston; were this remedied by throwing in more cold water the destruction of steam in the next filling of the cylinder would be proportionally increased. It has therefore in practice been found adviseable not to load these engines with columns of water weighing more than seven pounds for each square inch of the area of the piston. The bulk of water when converted into steam remained unknown until Mr. J. Watt, then of Glasgow, in 1764, determined it to be about 1800 times more rare than water. It soon occurred to Mr. Watt that a perfect engine would be that in which no steam should be condensed in filling the cylinder, and in which the steam should be so perfectly cooled as to produce nearly a perfect vacuum.

Mr. Watt having ascertained the degree of heat in which water boiled in vacuo, and under progressive degrees of pressure, and instructed by Dr. Black's discovery of latent heat, having calculated the quantity of cold water necessary to condense certain quantities of steam so far as to produce the exhaustion required, he made a communication from the cylinder to a cold vessel previously exhausted of air and water, into which the steam rushed by its elasticity, and became immediately condensed. He then adapted a cover to the cylinder and admitted steam above the piston to press it down instead of air, and instead of applying water he used oil or grease to fill the pores of the oakum and to lubricate the cylinder.

He next applied a pump to extract the injection water, the condensed steam, and the air, from the condensing vessel, every stroke of the engine.

To prevent the cooling of the cylinder by the contact of the external air, he surrounded it with a case containing steam, which he again protected by a covering of matters which conduct heat slowly.

This construction presented an easy means of regulating the power of the engine, for the steam being the acting power, as the pipe which admits it from the boiler is more or less opened, a greater or smaller quantity can enter during the time of a stroke, and consequently the engine can act with exactly the necessary degree of energy.

Mr. Watt gained a patent for his engine in 1768, but the further persecution of his designs were delayed by other avocations till 1775, when in conjunction with Mr. Boulton of Soho near Birmingham, numerous experiments were made on a large scale by their united ingenuity, and great improvements added to the machinery, and an act of parliament obtained for the prolongation of their patent for twenty-five years, they have since that time drained many of the deep mines in Cornwall, which but for the happy union of such genius must immediately have ceased to work. One of these engines works a pump of eighteen inches diameter, and upwards of 100 fathom or 600 feet high, at the rate of ten to twelve strokes of seven feet long each, in a minute, and that with one fifth part of the coals which a common engine would have taken to do the same work. The power of this engine may be easier comprehended by saying that it raised a weight equal to 81000 pounds 80 feet high in a minute, which is equal to the combined action of 200 good horses. In Newcomen's engine this would have required a cylinder of the enormous diameter of 120 inches or ten feet, but as in this engine of Mr. Watt and Mr. Boulton the steam acts, and a vacuum is made, alternately above and below the piston, the power exerted is double to what the same cylinder would otherways produce, and is further augmented by an inequality in the length of the two ends of the lever.

These gentlemen have also by other contrivances applied their engines to the turning of mills for almost every purpose, of which that great pile of machinery the Albion Mill is a well known instance. Forges, slitting mills, and other great works are erected where nature has furnished no running water, and future times may boast that this grand and useful engine was invented and perfected in our own country.

Since the above article went to the press the Albion Mill is no more; it is supposed to have been set on fire by interested or malicious incendaries, and is burnt to the ground. Whence London has lost the credit and the advantage of possessing the most powerful machine in the world!

NOTE XII.--FROST.

_In phalanx firm the fiend of Frost assail._

CANTO I. l. 439.

The cause of the expansion of water during its conversion into ice is not yet well ascertained, it was supposed to have been owing to the air being set at liberty in the act of congelation which was before dissolved in the water, and the many air bubbles in ice were thought to countenance this opinion. But the great force with which ice expands during its congelation, so as to burst iron bombs and coehorns, according to the experiments of Major Williams at Quebec, invalidates this idea of the cause of it, and may sometime be brought into use as a means of breaking rocks in mining, or projecting cannon-balls, or for other mechanical purposes, if the means of producing congelation should ever be discovered to be as easy as the means of producing combustion.

Mr. de Mairan attributes the increase of bulk of frozen water to the different arrangement of the particles of it in crystallization, as they are constantly joined at an angle of 60 degrees; and must by this disposition he thinks occupy a greater volume than if they were parallel. He found the augmentation of the water during freezing to amount to one-fourteenth, one-eighteenth, one-nineteenth, and when the water was previously purged of air to only one-twenty-second part. He adds that a piece of ice, which was at first only one-fourteenth part specifically lighter than water, on being exposed some days to the frost became one-twelfth lighter than water. Hence he thinks ice by being exposed to greater cold still increases in volume, and to this attributes the bursting of ice in ponds and on the glaciers. See Lewis's Commerce of Arts, p. 257. and the note on Muschus in the other volume of this work.

This expansion of ice well accounts for the greater mischief done by vernal frosts attended with moisture, (as by hoar-frosts,) than by the dry frosts called black frosts. Mr. Lawrence in a letter to Mr. Bradley complains that the dale-mist attended with a frost on may-day had destroyed all his tender fruits; though there was a sharper frost the night before without a mist, that did him no injury; and adds, that a garden not a stone's throw from his own on a higher situation, being above the dale-mist, had received no damage. Bradley, Vol. II. p. 232.

Mr. Hunter by very curious experiments discovered that the living principle in fish, in vegetables, and even in eggs and seeds, possesses a power of resisting congelation. Phil. Trans. There can be no doubt but that the exertions of animals to avoid the pain of cold may produce in them a greater quantity of heat, at least for a time, but that vegetables, eggs, or seeds, should possess such a quality is truly wonderful. Others have imagined that animals possess a power of preventing themselves from becoming much warmer than 98 degrees of heat, when immersed in an atmosphere above that degree of heat. It is true that the increased exhalation from their bodies will in some measure cool them, as much heat is carried off by the evaporation of fluids, but this is a chemical not an animal process. The experiments made by those who continued many minutes in the air of a room heated so much above any natural atmospheric heat, do not seem conclusive, as they remained in it a less time than would have been necessary to have heated a mass of beef of the same magnitude, and the circulation of the blood in living animals, by perpetually bringing new supplies of fluid to the skin, would prevent the external surface from becoming hot much sooner than the whole mass. And thirdly, there appears no power of animal bodies to produce cold in diseases, as in scarlet fever, in which the increased action of the vessels of the skin produces heat and contributes to exhaust the animal power already too much weakened.

It has been thought by many that frosts meliorate the ground, and that they are in general salubrious to mankind. In respect to the former it is now well known that ice or snow contain no nitrous particles, and though frost by enlarging the bulk of moist clay leaves it softer for a time after the thaw, yet as soon as the water exhales, the clay becomes as hard as before, being pressed together by the incumbent atmosphere, and by its self-attraction, called _setting_ by the potters. Add to this that on the coasts of Africa, where frost is unknown, the fertility of the soil is almost beyond our conceptions of it. In respect to the general salubrity of frosty seasons the bills of mortality are an evidence in the negative, as in long frosts many weakly and old people perish from debility occasioned by the cold, and many classes of birds and other wild animals are benumbed by the cold or destroyed by the consequent scarcity of food, and many tender vegetables perish from the degree of cold.

I do not think it should be objected to this doctrine that there are moist days attended with a brisk cold wind when no visible ice appears, and which are yet more disagreeable and destructive than frosty weather. For on these days the cold moisture, which is deposited on the skin is there evaporated and thus produces a degree of cold perhaps greater than the milder frosts. Whence even in such days both the disagreeable sensations and insalubrious effects belong to the cause abovementioned, viz. the intensity of the cold. Add to this that in these cold moist days as we pass along or as the wind blows upon us, a new sheet of cold water is as it were perpetually applied to us and hangs upon our bodies, now as water is 800 times denser than air and is a much better conductor of heat, we are starved with cold like those who go into a cold bath, both by the great number of particles in contact with the skin and their greater facility of receiving our heat.

It may nevertheless be true that snows of long duration in our winters may be less injurious to vegetation than great rains and shorter frosts, for two reasons. 1. Because great rains carry down many thousand pounds worth of the best part of the manure off the lands into the sea, whereas snow dissolves more gradually and thence carries away less from the land; any one may distinguish a snow-flood from a rain-flood by the transparency of the water. Hence hills or fields with considerable inclination of surface should be ploughed horizontally that the furrows may stay the water from showers till it deposits its mud. 2. Snow protects vegetables from the severity of the frost, since it is always in a state of thaw where it is in contact with the earth; as the earth's heat is about 48 deg. and the heat of thawing snow is 32 deg. the vegetables between them are kept in a degree of heat about 40, by which many of them are preserved. See note on Muschus, Vol. II. of this work.

NOTE XIII.--ELECTRICITY

_Cold from each point cerulean lustres gleam._

CANTO I. l. 339.

ELECTRIC POINTS.

There was an idle dispute whether knobs or points were preferable on the top of conductors for the defence of houses. The design of these conductors is to permit the electric matter accumulated in the clouds to pass through them into the earth in a smaller continued stream as the cloud approaches, before it comes to what is termed striking distance; now as it is well known that accumulated electricity will pass to points at a much greater distance than it will to knobs there can be no doubt of their preference; and it would seem that the finer the point and the less liable to become rusty the better, as it would take off the lightening while it was still at a greater distance, and by that means preserve a greater extent of building; the very extremity of the point should be of pure silver or gold, and might be branched into a kind of brush, since one small point can not be supposed to receive so great a quantity as a thicker bar might conduct into the earth.

If an insulated metallic ball is armed with a point, like a needle, projecting from one part of it, the electric fluid will be seen in the dark to pass off from this point, so long as the ball is kept supplied with electricity. The reason of this is not difficult to comprehend, every part of the electric atmosphere which surrounds the insulated ball is attracted to that ball by a large surface of it, whereas the electric atmosphere which is near the extremity of the needle is attracted to it by only a single point, in consequence the particles of electric matter near the surface of the ball approach towards it and push off by their greater gravitation the particles of electric matter over the point of the needle in a continued stream.

Something like this happens in respect to the diffusion of oil on water from a pointed cork, an experiment which was many years ago shewn me by Dr. Franklin; he cut a piece of cork about the size of a letter-wafer and left on one edge of it a point about a sixth of an inch in length projecting as a tangent to the circumference. This was dipped in oil and thrown on a pond of water and continued to revolve as the oil left the point for a great many minutes. The oil descends from the floating cork upon the water being diffused upon it without friction and perhaps without contact; but its going off at the point so forcibly as to make the cork revolve in a contrary direction seems analogous to the departure of the electric fluid from points.

Can any thing similar to either of these happen in respect to the earth's atmosphere and give occasion to the breezes on the tops of mountains, which may be considered as points on the earths circumference?

FAIRY-RINGS.

There is a phenomenon supposed to be electric which is yet unaccounted for, I mean the Fairy-rings, as they are called, so often seen on the grass. The numerous flashes of lightning which occur every summer are, I believe, generally discharged on the earth, and but seldom (if ever) from one cloud to another. Moist trees are the most frequent conductors of these flashes of lightning, and I am informed by purchasers of wood that innumerable trees are thus cracked and injured. At other times larger parts or prominences of clouds gradually sinking as they move along, are discharged on the moisture parts of grassy plains. Now this knob or corner of a cloud in being attracted by the earth will become nearly cylindrical, as loose wool would do when drawn out into a thread, and will strike the earth with a stream of electricity perhaps two or ten yards in diameter. Now as a stream of electricity displaces the air it passes through, it is plain no part of the grass can be burnt by it, but just the external ring of this cylinder where the grass can have access to the air, since without air nothing can be calcined. This earth after having been so calcined becomes a richer soil, and either funguses or a bluer grass for many years mark the place. That lightning displaces the air in its passage is evinced by the loud crack that succeeds it, which is owing to the sides of the aerial vacuum clapping together when the lightning is withdrawn. That nothing will calcine without air is now well understood from the acids produced in the burning of phlogistic substances, and may be agreeably seen by suspending a paper on an iron prong and putting it into the centre of the blaze of an iron-furnace; it may be held there some seconds and may be again withdrawn without its being burnt, if it be passed quickly into the flame and out again through the external part of it which is in contact with the air. I know some circles of many yards diameter of this kind near Foremark in Derbyshire which annually produce large white funguses and stronger grass, and have done so, I am informed, above thirty years. This increased fertility of the ground by calcination or charring, and its continuing to operate so many years is well worth the attention of the farmer, and shews the use of paring and burning new turf in agriculture, which produces its effect not so much by the ashes of the vegetable fibres as by charring the soil which adheres to them.

These situations, whether from eminence or from moisture, which were proper once to attract and discharge a thunder-cloud, are more liable again to experience the same. Hence many fairy-rings are often seen near each other either without intersecting each other, as I saw this summer in a garden in Nottinghamshire, or intersecting each other as described on Arthur's seat near Edinburgh in the Edinb. Trans. Vol. II. p. 3.

NOTE XIV.--BUDS AND BULBS.

_Where dwell my vegetative realms benumb'd In buds imprison'd, or in bulbs intomb'd._

CANTO I. l. 459.

A tree is properly speaking a family or swarm of buds, each bud being an individual plant, for if one of these buds be torn or cut out and planted in the earth with a glass cup inverted over it to prevent its exhalation from being at first greater than its power of absorption, it will produce a tree similar to its parent; each bud has a leaf, which is its lungs, appropriated to it, and the bark of the tree is a congeries of the roots of these individual buds, whence old hollow trees are often seen to have some branches flourish with vigour after the internal wood is almost intirely decayed and vanished. According to this idea Linneus has observed that trees and shrubs are roots above ground, for if a tree be inverted leaves will grow from the root-part and roots from the trunk-part. Phil. Bot p. 39. Hence it appears that vegetables have two methods of propagating themselves, the oviparous as by seeds, and the viviparous as by their buds and bulbs, and that the individual plants, whether from seeds or buds or bulbs, are all annual productions like many kinds of insects as the silk-worm, the parent perishing in the autumn after having produced an embryon, which lies in a torpid state during the winter, and is matured in the succeeding summer. Hence Linneus names buds and bulbs the winter-cradles of the plant or hybernacula, and might have given the same term to seeds. In warm climates few plants produce buds, as the vegetable life can be compleated in one summer, and hence the hybernacle is not wanted; in cold climates also some plants do not produce buds, as philadelphus, frangula, viburnum, ivy, heath, wood-nightshade, rue, geranium.

The bulbs of plants are another kind of winter-cradle, or hybernacle, adhering to the descending trunk, and are found in the perennial herbaceous plants which are too tender to bear the cold of the winter. The production of these subterraneous winter lodges, is not yet perhaps clearly understood, they have been distributed by Linneus according to their forms into scaly, solid, coated, and jointed bulbs, which however does not elucidate their manner of production. As the buds of trees may be truly esteemed individual annual plants, their roots constituting the bark of the tree, it follows that these roots (viz. of each individual bud) spread themselves over the last years bark, making a new bark over the old one, and thence descending cover with a new bark the old roots also in the same manner. A similar circumstance I suppose to happen in some herbaceous plants, that is, a new bark is annually produced over the old root, and thus for some years at least the old root or caudex increases in size and puts up new stems. As these roots increase in size the central