Chapter 2 of 4 · 8661 words · ~43 min read

part i

. pp. 192-194, where an illustration is given, and Paul Wetzger, _Die Flote_ (Heilbronn, 1906), pp. 23-24, and Tafel iv. No. 20.

FLUX (Lat. _fluxus_, a flowing; this being also the meaning of the English term in medicine, &c.), in metallurgy, a substance introduced in the smelting of ores to promote fluidity, and to remove objectionable impurities in the form of a slag. The substances in commonest use are:--lime or limestone, to slag off silica and silicates, fluor-spar for lead, calcium and barium sulphates and calcium phosphate, and silica for removing basic substances such as limestone. Other substances are also used, but more commonly in assaying than in metallurgy. Sodium and potassium carbonates are valuable for fluxing off silica; mixed with potassium nitrate sodium carbonate forms a valuable oxidizing fusion mixture; "black flux" is a reducing flux composed of finely divided carbon and potassium carbonate, and formed by deflagrating a mixture of argol with 1/4 to 1/2 its weight of nitre. Borax is very frequently employed; it melts to a clear liquid and dissolves silica and many metallic oxides. Potassium bisulphate is useful in the preliminary treatment of refractory aluminous ores. Litharge and red lead are used in silver and gold assays, acting as solvents for silica and any metallic oxides present.

FLY (formed on the root of the supposed original Teut. _fleugan_, to fly), a designation applied to the winged or perfect state of many insects belonging to various orders, as in butterfly (see LEPIDOPTERA), dragon-fly (q.v.), may-fly (q.v.), caddis-fly (q.v.), &c.; also specially employed by entomologists to mean any species of the two-winged flies, or Diptera (q.v.). In ordinary parlance _fly_ is often used in the sense of the common house-fly (_Musca domestica_); and by English colonists and sportsmen in South Africa in that of a species of tsetse-fly (_Glossina_), or a tract of country ("belt") in which these insects abound (see TSETSE-FLY).

Apart from the house-fly proper (_Musca domestica_), which in England is the usual one, several species of flies are commonly found in houses; e.g. the _Stomoxys calcitrans_, or stable-fly; _Pollenia rudis_, or cluster-fly; _Muscina stabulans_, another stable-fly; _Calliphora erythrocephala_, blue-bottle fly, blow-fly or meat-fly, with smaller sorts of blue-bottle, _Phormia terraenovae_ and _Lucilia caesar_; _Homalomyia canicularis_ and _brevis_, the small house-fly; _Scenopinus fenestralis_, the black window-fly, &c. But _Musca domestica_ is far the most numerous, and in many places, especially in hot weather and in hot climates, is a regular pest. Mr L.O. Howard (Circular 71 of the Bureau of Entomology U.S. Dept. of Agriculture, Washington, 1906) says that in 1900 he made a collection of the flies in dining-rooms in different parts of the United States, and out of a total of 23,087 flies, 22,808 were the common house-fly. Its geographical distribution is of the widest, and its rapidity of breeding, in manure and door-yard filth, so great that, as a carrier of germs of disease, especially cholera and typhoid, the house-fly is now recognized as a potent source of danger; and various sanitary regulations have been made, or precautions suggested, for getting rid of it. These are discussed by Mr Howard in the paper referred to, but in brief they all amount to measures of general hygiene, and the isolation, prompt removal, or proper sterilization of the animal or human excrement in which these flies breed.

FLYCATCHER, a name introduced in ornithology by Ray, being a translation of the _Muscicapa_ of older authors, and applied by Pennant to an extremely common English bird, the _M. grisola_ of Linnaeus. It has since been used in a general and very vague way for a great many small birds from all parts of the world, which have the habit of catching flies on the wing. Ornithologists who have trusted too much to this characteristic and to certain merely superficial correlations of structure, especially those exhibited by a broad and rather flat bill and a gape beset by strong hairs or bristles, have associated under the title of _Muscicapidae_ an exceedingly heterogeneous assemblage of forms much reduced in number by later systematists. Great advance has been made in establishing as independent families the _Todidae_ and _Eurylaemidae_, as well as in excluding from it various members of the _Ampelidae_, _Cotingidae_, _Tyrannidae_, _Vireonidae_, _Mniotiltidae_, and perhaps others, which had been placed within its limits. These steps have left the _Muscicapidae_ a purely Old-World family of the order _Passeres_, and the chief difficulty now seems to lie in separating it from the _Campephagidae_ and the _Laniidae_. Only a very few of the forms of flycatchers (which, after all the deductions above mentioned, may be reckoned to include some 60 genera or subgenera, and perhaps 250 species) can here be even named.[1]

The best-known bird of this family is that which also happens to be the type of the Linnaean genus _Muscicapa_--the spotted or grey flycatcher (_M. grisola_). It is a common summer visitant to nearly the whole of Europe, and is found throughout Great Britain, though less abundant in Scotland than in England, as well as in many parts of Ireland, where, however, it seems to be but locally and sparingly distributed. It is one of the latest migrants to arrive, and seldom reaches the British Islands till the latter part of May, when it may be seen, a small dust-coloured bird, sitting on the posts or railings of gardens and fields, ever and anon springing into the air, seizing with an audible snap of its bill some passing insect as it flies, and returning to the spot it has quitted, or taking up some similar station to keep watch as before. It has no song, but merely a plaintive or peevish call-note, uttered from time to time with a jerking gesture of the wings and tail. It makes a neat nest, built among the small twigs which sprout from the bole of a large tree, fixed in the branches of some plant trained against a wall, or placed in any hole of the wall itself that may be left by the falling of a brick or stone. The eggs are from four to six in number, of a pale greenish-blue, closely blotched or freckled with rust-colour. Silent and inconspicuous as is this bird, its constant pursuit of flies in the closest vicinity of houses makes it a familiar object to almost everybody. A second British species is the pied flycatcher (_M. atricapilla_), a much rarer bird, and in England not often seen except in the hilly country extending from the Peak of Derbyshire to Cumberland, and more numerous in the Lake District than elsewhere. It is not common in Scotland, and has only once been observed in Ireland. More of a woodland bird than the former, the brightly-contrasted black and white plumage of the cock, together with his agreeable song, readily attracts attention where it occurs. It is a summer visitant to all western Europe, but farther eastward its place is taken by a nearly allied species (_M. collaris_) in which the white of the throat and breast extends like a collar round the neck. A fourth European species (_M. parva_), distinguished by its very small size and red breast, has also strayed some three or four times to the extreme south-west of England. This last belongs to a group of more eastern range, which has received generic recognition under the name of _Erythrosterna_, and it has several relations in Asia and particularly in India, while the allies of the pied flycatchers (_Ficedula_ of Brisson) are chiefly of African origin, and those of the grey or spotted flycatcher (_Muscicapa_ proper[2]) are common to the two continents.

One of the most remarkable groups of _Muscicapidae_ is that known as the paradise flycatchers, forming the genus _Tchitrea_ of Lesson. In nearly all the species the males are distinguished by the growth of exceedingly long feathers in their tail, and by their putting on, for some part of the year at least, a plumage generally white, but almost always quite different from that worn by the females, which is of a more or less deep chestnut or bay colour, though in both sexes the crown is of a glossy steel-blue. They are found pretty well throughout Africa and tropical Asia to Japan, and seem to affect the deep shade of forests rather than the open country. The best-known species is perhaps the Indian _T. paradisi_; but the Chinese _T. incii_, and the Japanese _T. princeps_, from being very commonly represented by the artists of those nations on screens, fans and the like, are hardly less so; and the cock of the last named, with his bill of a pale greenish-blue and eyes surrounded by bare skin of the same colour--though these are characters possessed in some degree by all the species--seems to be the most beautiful of the genus. _T. bourbonnensis_, which is peculiar to the islands of Mauritius and Reunion, appears to be the only species in which the outward difference of the sexes is but slight. In _T. corvina_ of the Seychelles, the adult male is wholly black, and his middle tail-feathers are not only very long but very broad. In _T. mutata_ of Madagascar, some of the males are found in a blackish plumage, though with the elongated median rectrices white, while in others white predominates over the whole body; but whether this sex is here actually dimorphic, or whether the one dress is a passing phase of the other, is at present undetermined. Some of the African species, of which many have been described, seem always to retain the rufous plumage, but the long tail-feathers serve to mark the males.

A few other groups are distinguished by the brilliant blue they exhibit, as _Myiagra azurea_, and others as _Monarcha_ (or _Arses_) _chrysomela_ by their golden yellow. The Australian forms assigned to the _Muscicapidae_ are very varied. _Sisura inquieta_ has some of the habits of a water-wagtail (_Motacilla_), and hence has received the name of "dishwasher," bestowed in many parts of England on its analogue; and the many species of _Rhipidura_ or fantailed flycatchers, which occur in various parts of the Australian Region, have manners still more singular--turning over in the air, it is said, like a tumbler pigeon, as they catch their prey; but concerning the mode of life of the majority of the _Muscicapidae_, and especially of the numerous African forms, hardly anything is known. (A. N.)

FOOTNOTES:

[1] Of the 30 genera or subgenera which Swainson included in his _Natural Arrangement and Relations of the Family of Flycatchers_ (published in 1838), at least 19 do not belong to the _Muscicapidae_ at all, and one of them, _Todus_, not even to the order _Passeres_. It is perhaps impossible to name any ornithological work whose substance so fully belies its title as does this treatise. Swainson wrote it filled with faith in the so-called "Quinary System"--that fanciful theory, invented by W.S. Macleay, which misled and kept back so many of the best English zoologists of his generation from the truth,--and, unconsciously swayed by his bias, his judgment was warped to fit his hypothesis.

[2] By some writers this section is distinguished as _Butalis_ of Boie, but to do so seems contrary to rule.

FLYGARE-CARLEN, EMILIE (1807-1892), Swedish novelist, was born in Stromstad on the 8th of August 1807. Her father, Rutger Smith, was a retired sea-captain who had settled down as a small merchant, and she often accompanied him on the voyages he made along the coast. She married in 1827 a doctor named Axel Flygare, and went with him to live in the province of Smaland. After his death in 1833 she returned to her old home and published in 1838 her first novel, _Waldemar Klein_. In the next year she removed to Stockholm, and married, in 1841, the jurist and poet, Johan Gabriel Carlen (1814-1875). Her house became a meeting-place for Stockholm men of letters, and for the next twelve years she produced one or two novels annually. The premature death of her son Edvard Flygare (1829-1853), who had already published three books, showing great promise, was followed by six years of silence, after which she resumed her writing until 1884. The most famous of her tales are _Rosen pa Tistelon_ (1842; Eng. trans. _The Rose of Tistelon_, 1842); _Enslingen pa Johannesskaret_ (1846; Eng. trans. _The Hermit_, 4 vols., 1853); and _Ett Kopemanshus i skargarden_ (1859; _The Merchant's House on the Cliffs_). Fru Carlen published in 1878 _Minnen af svenskt forfattarlif_ 1840-1860, and in 1887-1888 three volumes of _Efterskord fran en 80- arings forfattarbana_, containing her last tales. She died at Stockholm on the 5th of February 1892. Her daughter, Rosa Carlen (1836-1883), was also a popular novelist.

Emilie Flygare-Carlen's novels were collected in thirty-one volumes (Stockholm, 1869-1875).

FLYING BUTTRESS, in architecture, the term given to a structural feature employed to transmit the thrust of a vault across an intervening space, such as an aisle, chapel or cloister, to a buttress built outside the latter. This was done by throwing a semi-arch across to the vertical buttress. Though employed by the Romans and in early Romanesque work, it was generally masked by other constructions or hidden under a roof, but in the 12th century it was recognized as rational construction and emphasized by the decorative accentuation of its features, as in the cathedrals of Chartres, Le Mans, Paris, Beauvais, Reims, &c. Sometimes, owing to the great height of the vaults, two semi-arches were thrown one above the other, and there are cases where the thrust was transmitted to two or even three buttresses across intervening spaces. As a vertical buttress, placed at a distance, possesses greater power of resistance to thrust than if attached to the wall carrying the vault, vertical buttresses as at Lincoln and Westminster Abbey were built outside the chapterhouse to receive the thrust. All vertical buttresses are, as a rule, in addition weighted with pinnacles to give them greater power of resistance.

FLYING COLUMN, in military organization, an independent corps of troops usually composed of all arms, to which a particular task is assigned. It is almost always composed in the course of operations, out of the troops immediately available. Mobility being its _raison d'etre_, a flying column is when possible composed of picked men and horses accompanied with the barest minimum of baggage. The term is usually, though not necessarily, applied to forces under the strength of a brigade. The "mobile columns" employed by the British in the South African War of 1899-1902, were usually of the strength of two battalions of infantry, a battery of artillery, and a squadron of cavalry--almost exactly half that of a mixed brigade. Flying columns are mostly used in savage or guerrilla warfare.

"FLYING DUTCHMAN," a spectre-ship popularly believed to haunt the waters around the Cape of Good Hope. The legend has several variants, but the commonest is that which declares that the captain of the vessel, Vanderdecken, was condemned for his blasphemy to sail round the cape for ever, unable to "make" a port. In the Dutch version the skipper is the ghost of the Dutch seaman Van Straaten. The appearance of the "Flying Dutchman" is considered by sailors as ominous of disaster. The German legend makes one Herr Von Falkenberg the hero, and alleges that he is condemned to sail for ever around the North Sea, on a ship without helm or steersman, playing at dice for his soul with the devil. Sir Walter Scott says the "Flying Dutchman" was originally a vessel laden with bullion. A murder was committed on board, and thereafter the plague broke out among the crew, which closed all ports to the ill-fated craft. The legend has been used by Wagner in his opera _Der fliegende Hollander_.

FLYING-FISH, the name given to two different kinds of fish. The one (_Dactylopterus_) belongs to the gurnard family (_Triglidae_), and is more properly called flying gurnard; the other (_Exocoetus_) has been called flying herring, though more nearly allied to the gar-pike than to the herring. Some other fishes with long pectoral fins (_Pterois_) have been stated to be able to fly, but this has been proved to be incorrect.

[Illustration: FIG. 1.--_Dactylopterus volitans._]

The flying gurnards are much less numerous than the _Exocoeti_ with regard to individuals as well as species, there being only three or four species known of the former, whilst more than fifty have been described of the latter, which, besides, are found in numerous shoals of thousands. The _Dactylopteri_ may be readily distinguished by a large bony head armed with spines, hard keeled scales, two dorsal fins, &c. The _Exocoeti_ have thin, deciduous scales, only one dorsal fin, and the ventrals placed far backwards, below the middle of the body; some have long barbels at the chin. In both kinds the pectoral fins are greatly prolonged and enlarged, modified into an organ of flight, and in many species of _Exocoetus_ the ventral fins are similarly enlarged, and evidently assist in the aerial evolutions of these fishes. Flying-fishes are found in the tropical and sub-tropical seas only, and it is a singular fact that the geographical distribution of the two kinds is nearly identical. Flying-fish are more frequently observed in rough weather and in a disturbed sea than during calms; they dart out of the water when pursued by their enemies or frightened by an approaching vessel, but frequently also without any apparent cause, as is also observed in many other fishes; and they rise without regard to the direction of the wind or waves. The fins are kept quietly distended, without any motion, except an occasional vibration caused by the air whenever the surface of the wing is parallel with the current of the wind. Their flight is rapid, greatly exceeding that of a ship going 10 m. an hour, but gradually decreasing in velocity and not extending beyond a distance of 500 ft. Generally it is longer when the fishes fly against, than with or at an angle to, the wind. Any vertical or horizontal deviation from a straight line is not caused at the will of the fish, but by currents of the air; thus they retain a horizontally straight course when flying with or against the wind, but are carried towards the right or left whenever the direction of the wind is at an angle with that of their flight. However, it sometimes happens that the fish during its flight immerses its caudal fin in the water, and by a stroke of its tail turns towards the right or left. In a calm the line of their flight is always also vertically straight or rather parabolic, like the course of a projectile, but it may become undulated in a rough sea, when they are flying against the course of the waves; they then frequently overtop each wave, being carried over it by the pressure of the disturbed air. Flying-fish often fall on board of vessels, but this never happens during a calm or from the lee side, but during a breeze only and from the weather side. In day time they avoid a ship, flying away from it, but during the night when they are unable to see, they frequently fly against the weather board, where they are caught by the current of the air, and carried upwards to a height of 20 ft. above the surface of the water, whilst under ordinary circumstances they keep close to it. All these observations point clearly to the fact that any deflection from a straight course is due to external circumstances, and not to voluntary action on the part of the fish.

[Illustration: FIG. 2.--_Exocoetus callopterus._]

A little Malacopterygian fish about 4 in. long has recently been discovered in West Africa which has the habits of a fresh-water flying-fish. It has been named _Pantodon buchholzi_. It has very large pectoral fins with a remarkable muscular process attached to the inner ray. It lives in fresh-water lakes and rivers in the Congo region, and has been caught in its flight above the water in a butterfly-net.

FLYING-FOX, or, more correctly, FOX-BAT. The first name is applied by Europeans in India to the fruit-eating bats of the genus _Pteropus_, which contains more than half the family (_Pteropidae_). This genus is confined to the tropical regions of the Eastern hemisphere and Australia. It comprises numerous species, a considerable proportion of which occur in the islands of the Malay Archipelago. The flying-foxes are the largest of the bats, the kalong of Java (_Pteropus edulis_) measuring about a foot in length, and having an expanse of wing-membrane measuring 5 ft. across. Flying-foxes are gregarious, nocturnal bats, suspending themselves during the day head-downwards by thousands from the branches of trees, where with their wings gathered about them, they bear some resemblance to huge shrivelled-up leaves or to clusters of some peculiar fruit. In Batchian, according to Wallace, they suspend themselves chiefly from the branches of dead trees, where they are easily caught or knocked down by sticks, the natives carrying them home in basketfuls. They are then cooked with abundance of spices, and "are really very good eating, something like hare." Towards evening these bats bestir themselves, and fly off in companies to the village plantations, where they feed on all kinds of fruit, and so numerous and voracious are they that no garden crop has much chance of being gathered which is not specially protected from their attacks. The flying-fox of India (_Pteropus medius_) is a smaller species, but is found in great numbers wherever fruit is to be had in the Indian peninsula.

FLYING-SQUIRREL, properly the name of such members of the squirrel-group of rodent mammals as have a parachute-like expansion of the skin of the flanks, with attachments to the limbs, by means of which they are able to take long flying-leaps from tree to tree. The parachute is supported by a cartilage attached to the wrist or carpus; in addition to the lateral membrane, there is a narrow one from the cheek along the front of each shoulder to the wrist, and in the larger species a third (interfemoral) connecting the hind-limbs with the base of the long tail. Of the two widely distributed genera, _Pteromys_ includes the larger and _Sciuropterus_ the smaller species. The two differ in certain details of dentition, and in the greater development in the former of the parachute, especially the interfemoral portion, which in the latter is almost absent. In _Pteromys_ the tail is cylindrical and comparatively thin, while in _Sciuropterus_ it is broad, flat and laterally expanded, so as to compensate for the absence of the interfemoral membrane by

## acting as a supplementary parachute.

[Illustration: Pigmy African Flying-Squirrel (_Idiurus zenkeri_).]

In general appearance flying-squirrels resemble ordinary squirrels, although they are even more beautifully coloured. Their habits, food, &c., are also very similar to those of the true squirrels, except that they are more nocturnal, and are therefore less often seen. The Indian flying-squirrel (_P. oral_) leaps with its parachute extended from the higher branches of a tree, and descends first directly and then more and more obliquely, until the flight, gradually becoming slower, assumes a horizontal direction, and finally terminates in an ascent to the branch or trunk of the tree to which it was directed. The presence of these rodents at night is made known by their screaming cries. _Sciuropterus_ is represented by _S. velucella_ in eastern Europe and northern Asia, and by a second species in North America, but the other species of this genus and all those of _Pteromys_ are Indo-Malayan. A third genus, _Eupetaurus_, typified by a very large, long-haired, dark-grey species from the mountains to the north-west of Kashmir (_Eu. cinereus_), differs from all other members of the squirrel-family by its tall-crowned molar teeth. It has a total length of 37 in., of which 22 are taken up by the tail.

In Africa the name of flying-squirrel is applied to the members of a very different family of rodents, the _Anomaluridae_, which are provided with a parachute. Since, however, this parachute is absent in some members of the family, the most distinctive character is the presence of a double row of spiny scales on the under surface of the tail, which apparently aid in climbing. The flying species are also distinguished from ordinary flying-squirrels by the circumstance that the additional bone serving for the support of the fore part of the flying-membrane rises from the elbow-joint instead of from the wrist. The family is represented by two flying genera, _Anomalurus_ and _Idiurus_; the latter containing only one very minute species (shown in the cut) characterized by its small ears and elongated tail. Most of the species are West African. In habits these rodents appear to be very similar to the true flying-squirrels. The species without a parachute constitutes the genus _Zenkerella_, and looks very like an ordinary squirrel (see RODENTIA).

In Australia and Papua the name flying-squirrel is applied to such marsupials as are provided with parachutes; animals which naturalists prefer to designate flying-phalangers (see MARSUPIALIA) (R. L.*)

FLYSCH, in geology, a remarkable formation, composed mainly of sandstones, soft marls and sandy shales found extending from S.W. Switzerland eastward along the northern Alpine zone to the Vienna basin, whence it may be followed round the northern flanks of the Carpathians into the Balkan peninsula. It is represented in the Pyrenees, the Apennines, the Caucasus and extends into Asia; similar flysch-like deposits are related to the Himalayas as the European formations are to the Alps. The Flysch is not of the same age in every place; thus in the western parts of Switzerland the oldest portions probably belong to the Eocene period, but the principal development is of Oligocene age; as it is traced eastward we find in the east Alps that it descends into the upper Cretaceous, and in the Vienna region and the Carpathians it contains intercalations which clearly indicate a lower Cretaceous horizon for the lower parts. It appears indeed that this type of formation was in progress of deposition at one point or another in the regions enumerated above from Jurassic to late Tertiary times. The absence of fossils from enormous thicknesses of Flysch makes the correlation with other formations difficult; often the only indications of organisms are the abundant markings supposed to represent Algae (Chondrites, &c.), which have given rise to the term "Hieroglyphic-sandstone." The most noteworthy exceptions are perhaps the Oligocene fish-bed of Glarus, the Eocene nummulitic beds in Calabria, and the _Aptychus_ beds of Waidhofen. Local phases of the Flysch have received special names; it is the "Vienna" or "Carpathian" sandstone of those regions; the "macigno" (a soft sandstone with calcareous cement) of the Maritime Alps and Apennines; the "scagliose" (scaly clays) and "alberese" (limestones) of the same places are portions of this formation. The _gris de Menton_, the _gris d'Annot_ of the Basses Alps, and the _gris d'Embrun_ of Chaillot appear in Switzerland as the _gris de Taveyannaz_. At several places the upper layers of the Flysch are iron-stained, as in the region of Leman and at the foot of the Dent du Midi; it is then styled the "Red-Flysch." Lenticular intercalations of gabbro, diabase, &c., occur in the Flysch in Calabria on the Pyrenees. Large exotic blocks of granite, gneiss and other crystalline rocks in coarse conglomerates are found near Vienna, near Sonthofen in Bavaria, near Lake Thun (Wild Flysch) and at other points, which have been variously regarded as indications of glaciation or of coastal conditions.

FOCA (pronounced _Fawtcha_), a town of Bosnia, situated at the confluence of the Drina and Cehotina rivers, and encircled by wooded mountains. Pop. (1895) 4217. The town is the headquarters of a thriving industry in silver filigree-work and inlaid weapons, for which it was famous. With its territories enclosed by the frontiers of Montenegro and Novi Bazar, Foca, then known as _Chocha_, was the scene of almost incessant border warfare during the middle ages. No monuments of this period are left except the Bogomil cemeteries, and the beautiful mosques, which are the most ancient in Bosnia. The three adjoining towns of Foca, Gorazda and Ustikolina were trading-stations of the Ragusans in the 14th century, if not earlier. In the 16th century, Benedetto Ramberti, ambassador from Venice to the Porte, described the town, in his _Libri Tre delle Cose dei Turchi_, as _Cozza_, "a large settlement, with good houses in Turkish style, and many shops and merchants. Here dwells the governor of Herzegovina, whose authority extends over the whole of Servia. Through this place all goods must pass, both going and returning, between Ragusa and Constantinople."

FOCHABERS, a burgh of barony and village of Elginshire, Scotland. Pop. (1901) 981. It is delightfully situated on the Spey, about 9 m. E. by S. of Elgin, the terminus of a branch of the Highland railway connecting at Orbliston Junction with the main line from Elgin to Keith. The town was rebuilt in its present situation at the end of the 18th century, when its earlier site was required for alterations in the grounds of Gordon Castle, in which the old town cross still stands. The streets all lead at right angles to the central square, where fairs and markets are held. The public buildings include a library and reading-room, the court-house and the Milne school, named after Alexander Milne, who endowed it with a legacy of L20,000. Adjoining the town, surrounded by a park containing many magnificent old trees, stands Gordon Castle, the chief seat of the duke of Richmond and Gordon, erected in the 18th century. The antiquary George Chalmers (1742-1825) and the composer William Marshall (1748-1833) were natives of the burgh.

FOCSHANI (Rumanian _Focsani_, sometimes incorrectly written _Fokshani_ or _Fokshan_), the capital of the department of Putna, Rumania; on the river Milcov, which formed the ancient frontier of the former principalities of Moldavia and Walachia. Pop. (1900) 23,783; of whom 6000 were Jews. The chief buildings are the prefecture, schools, synagogues, and many churches, including those of the Armenians and Protestants. Focshani is a commercial centre of some importance, the chief industries being oil and soap manufacture and tannery. A large wine trade is also carried on, and corn is shipped in lighters to Galatz. The annual fair is held on the 29th of April. Government explorations in the vicinity of this town show it to be rich in minerals, such as iron, copper, coal and petroleum. The line Focshani-Galatz is covered by a very strong line of fortifications, known as the Sereth Line. A congress between Russian and Turkish diplomatists was held near the town in 1772. In the neighbourhood the Turks suffered a severe defeat from the Austrians and Russians in 1789.

FOCUS (Latin for "hearth" or "fireplace"), a point at which converging rays meet, toward which they are directed, or from which diverging rays are directed; in the latter case called the virtual focus (see MICROSCOPE; TELESCOPE; LENS). In geometry the word is used to denote certain points (see GEOMETRY; CONIC SECTION; and PERSPECTIVE).

FOG, the name given to any distribution of solid or liquid particles in the surface layers of the atmosphere which renders surrounding objects notably indistinct or altogether invisible according to their distance. In its more intense forms it hinders and delays travellers of all kinds, by sea or land, by railway, road or river, or by the mountain path. It is sometimes so thick as to paralyse traffic altogether. According to the _New English Dictionary_ the word "appears to be" a back formation from the adjective "foggy," a derivative of "fog" used with its old meaning of aftermath or coarse grass, or, in the north of Britain, of "moss." Such a formation would be reasonable, because wreaths of fog in the atmospheric sense are specially characteristic of meadows and marshes where fog, in the more ancient sense, grows.

Two other words, _mist_ and _haze_, are also in common use with reference to the deterioration of transparency of the surface layers of the atmosphere caused by solid or liquid particles, and in ordinary literature the three words are used almost according to the fancy of the writer. It seems possible to draw a distinction between mist and haze that would be fairly well supported by usage. Mist may be defined as a cloud of water particles at the surface of land or sea, and would only occur when the air is nearly or actually saturated, that is, when there is little or no difference between the readings of the dry and wet bulbs; the word haze, on the other hand, may be reserved for the obscuration of the surface layers of the atmosphere when the air is dry.

It would not be difficult to quote instances in which even this distinction is disregarded in practice. Indeed, the telegraphic code of the British Meteorological Office uses the same figure for mist and haze, and formerly the Beaufort weather notation had no separate letter for haze (now indicated by z), though it distinguished between f, fog, and m, mist. It is possible, however, that these practices may arise, not from confusion of idea, but from economy of symbols, when the meaning can be made out from a knowledge of the associated observations.

As regards the distinction between mist and fog, careful consideration of a number of examples leads to the conclusion that the word "fog" is used to indicate not so much the origin or meteorological nature of the obscurity as its effect upon traffic and travellers whether on land or sea. It is, generally speaking, "in a fog" that a traveller loses himself, and indeed the phrase has become proverbial in that sense. A "fog-bell" or "fog-horn" is sounded when the atmosphere is so thick that the aid of sound is required for navigation. A vessel is "fog-logged" or "fog-bound" when it is stopped or detained on account of thick atmosphere. A "fog-signal" is employed on railways when the ordinary signals are obliterated within working distances. A "fog-bow" is the accompaniment of conditions when a mountain traveller is apt to lose his way.

These words are used quite irrespective of the nature of the cloud which interferes with effective vision and necessitates the special provision; the word "mist" is seldom used in similar connexion. We may thus define a fog as a surface cloud sufficiently thick to cause hindrance to traffic. It will be a _thick mist_ if the cloud consists of water

## particles, a _thick haze_ if it consists of smoke or dust particles

which would be persistent even in a dry atmosphere.

It is probable that sailors would be inclined to restrict the use of the word to the surface clouds met with in comparatively calm weather, and that the obscurity of the atmosphere when it is blowing hard and perhaps raining hard as well should be indicated by the terms "thick weather" or "very thick weather" and not by "fog"; but the term "fog" would be quite correctly used on such occasions from the point of view of cautious navigation. If cloud, drizzling rain, or heavy rain cause such obscurity that passing ships are not visible within working distances the sounding of a fog-horn becomes a duty.

The number of occasions upon which fog and mist may be noted as occurring with winds of different strengths may be exemplified by the following results of thirty years for St Mary's, Scilly Isles, where the observations have always been made by men of nautical experience.

+----------------------------+-----+---+---+---+---+---+----+----+-------+ | Wind Force. |0 & 1| 2 | 3 | 4 | 5 | 6 | 7 |8-12| All | | | | | | | | | | | Winds.| +----------------------------+-----+---+---+---+---+---+----+----+-------+ |Number of occasions of fog | | | | | | | | | | | per 1000 observations | 8 | 7 | 9 |14 | 6 | 3 | <1 | <1 | 47 | |Number of occasions of mist | | | | | | | | | | | per 1000 observations | 5 | 6 |11 |22 |20 |12 | 6 | 2 | 84 | +----------------------------+-----+---+---+---+---+---+----+----+-------+

The use of the word "fog" in the connexion "high fog," to describe the almost total darkness in the daytime occasionally noted in London and other large cities due to the persistent opaque cloud in the upper air without serious obscuration of the surface layers, is convenient but incorrect.

Regarding "fog" as a word used to indicate the state of the atmosphere as regards transparency considered with reference to its effect upon traffic, a scale of fog intensity has been introduced for use on land or at sea, whereby the intensity of obscurity is indicated by the numbers 1 to 5 in the table following. At sea or in the country a fog, as a rule, is white and consists of a cloud of minute water globules, of no great vertical thickness, which disperses the sunlight by repeated reflection but is fully translucent. In dust-storms and sand-storms dark or coloured fog clouds are produced such as those which are met with in the Harmattan winds off the west coast of Africa. In large towns the fog cloud is darkened and intensified by smoke, and in some cases may be regarded as due entirely to the smoke.

_Description of Effects._

The physical processes which produce fogs of water particles are complicated and difficult to unravel. We have to account for the formation and maintenance of a cloud at the earth's surface; and the process of cloud-formation which is probably most usual in nature, namely, the cooling of air by rarefaction due to the reduction of pressure on ascent, cannot be invoked, except in the case of the fogs forming the cloud-caps of hills, which are perhaps not fairly included. We have to fall back upon the only other process hitherto recognized as causing cloudy condensation in the atmosphere, that is to say, the mixing of masses of mist air of different temperatures. The mixing is brought about by the slow motion of air masses, and this slow motion is probably essential to the phenomenon.

TABLE I.--_Air travelling from Northern Africa to Northern Russia, round by the Azores._

+------------------------------------+---------+---------+---------+---------+-----------+ | Successive Temperatures of sea | 68 deg. | 68 deg. | 67 deg. | 59 deg. | 54 deg. F.| | " " " air | 68 deg. | 70 deg. | 67 deg. | 60 deg. | 56 deg. F.| | " States of the atmosphere | clear | clear | clear | shower | mist | +------------------------------------+---------+---------+---------+---------+-----------+

TABLE II.--_Air travelling from N.W. Africa to Scotland._

+-------------------------------+---------+---------+-----------------+ |Successive Temperatures of sea | 67 deg. | 63 deg. | 54 deg. F. | | " " " air | 66 deg. | 64 deg. | 53 deg. F. | | " State of atmosphere | fair | shower | mist with shower| +-------------------------------+---------+---------+-----------------+

Over the sea fog is most frequently due to the cooling of a surface layer of warm air by the underlying cold water. The amount of motion of the air must be sufficient to prevent the condensation taking place at the sea surface without showing itself as a cloud. In a research on the Life History of Surface Air Currents the changes incidental to the movement of the air over the north Atlantic Ocean were traced with great care, and the above examples (Tables I, II) taken from page 72 of the work referred to are typical of the formation of sea fog by the cooling of a relatively warm current passing over cold water.

In conformity with this suggestion we find that fog is most liable to occur over the open ocean in those regions where, as off the Newfoundland banks, cold-water currents underlie warm air, and that it is most frequent at the season of the year when the air temperature is increasing faster than the water temperature. But it is difficult to bring this hypothesis always to bear upon actual practice, because the fog is representative of a temperature difference which has ceased to exist. One cannot therefore observe under ordinary circumstances both the temperature difference and the fog. Doubtless one requires not only the initial temperature difference but also the slow drift of air which favours cooling of the lower layers without too much mixing and consequently a layer of fog close to the surface. Such a fog, the characteristic sea fog, may be called a cold surface fog. From the conditions of its formation it is likely to be less dense at the mast-head than it is on deck.

One would expect that a cold-air current passing over a warm sea surface would give rise to an ascending current of warmed air and hence cause cumulus cloud and possibly thunder showers rather than surface fog, but one cannot resist the conclusion that sea fog is sometimes formed by slow transference of cold air over relatively warm water, giving rise to what may be called a "steaming-pot" fog. In such a case the actual surface layer in contact with the warm water would be clear, and the fog would be thicker aloft where the mixing of cold air and water vapour is more complete. Such fogs are, however, probably rare in comparison with the cold-water fogs. If the existence of a cold current over warm water were a sufficient cause of fog, as a current of warm air over cold water appears to be, the geographical distribution of notable fog would be much more widespread than it actually is, and the seasonal distribution of fog would also be other than it is.

The formation of fog over land seems to be an even more complicated process than over the sea. Certainly in some cases mistiness amounting to fog arises from the replacement of cold surface air which has chilled the earth and the objects thereon by a warm current. But this process can hardly give rise to detached masses or banks of fog. The ordinary land or valley fog of the autumn evening or winter morning is due to the combination of three causes, first the cooling of the surface layer of air at or after sunset by the radiation of the earth, or more

## particularly of blades of grass, secondly the slow downward flow (in the

absence of wind) of the air thus cooled towards lower levels following roughly the course of the natural water drainage of the land, and thirdly the supply of moisture by evaporation from warm moist soil or from the relatively warm water surface of river or lake. In this way steaming-pot fog gradually forms and is carried downward by the natural though slow descent of the cooled air. It thus forms in wreaths and banks in the lowest parts, until perhaps the whole valley becomes filled with a cloud of mist or fog. A case of this kind in the Lake District is minutely described by J.B. Cohen (_Q.J. Roy. Met. Soc._ vol. 30, p. 211, 1904).

It will be noticed that upon this hypothesis the circumstances favourable for fog formation are (1) a site near the bottom level of the drainage area, (2) cold surface air and no wind, (3) an evening or night of vigorous radiation, (4) warm soil, and (5) abundant moisture in the surface-soil. These conditions define with reasonable accuracy the circumstances in which fog is actually observed.

The persistence of these fog wreaths is always remarkable when one considers that the particles of a fog cloud, however small they may be, must be continually sinking through the air which holds them, and that unless some upward motion of the air keeps at least a balance against this downward fall, the particles of the cloud must reach the earth or water and to that extent the cloud must disappear. In sheltered valleys it is easy to suppose that the constant downward drainage of fresh and colder fog-laden material at the surface supplies to the layers displaced from the bottom the necessary upward motion, and the result of the gradual falling of drops is only that the surface cloud gets thicker; but there are occasions when the extent and persistence of land fog seems too great to be accounted for by persistent radiation cooling. For example, in the week before Christmas of 1904 the whole of England south of the Humber was covered with fog for several days. It is of course possible that so much fog-laden air was poured down from the sides of mountains and hills that did project above the surface of the fog, as to keep the lower reaches supplied for the whole time, but without more particulars such a statement seems almost incredible. Moreover, the drifting of fog banks over the sea seems capricious and unrelated to any known circumstances of fog-formation, so that one is tempted to invoke the aid of electrification of the particles or some other abnormal condition to account for the persistence of fog. The observations at Kew observatory show that the electrical potential is abnormally high during fog, but whether that is the cause or the result of the presence of the water particles, we are not yet in a position to say. It must be remembered that a fog cloud ought to be regarded as being, generally speaking, _in process of formation_ by mixing. Observations upon clouds formed experimentally in globes tend to show that if a mass of fog-bearing air could be enclosed and kept still for only a short while the fog would settle and leave the air clear. The apparently capricious behaviour of fog banks may be due to the fact that mixing is still going on in the persistent ones, but is completed in the disappearing ones.

One remarkable characteristic of a persistent fog is the coldness of the foggy air at the surface in spite of the heat of the sun's rays falling upon the upper surface of the fog. A remarkable example may be quoted from the case of London, which was under fog all day on 28th January 1909. The maximum temperature only reached 31 deg. F., whereas at Warlingham in Surrey from which the fog lifted it was as high as 46 deg. F.

_A priori_ we might suppose that the formation of fog would arrest cooling by radiation, and that fog would thus act as a protection of plants against frost. The condensation of water evaporated from wet ground, which affords the material for making fog, does apparently act as a protection, and heavy watering is sometimes used to protect plants from frost, but the same cannot be said of fog itself--cooling appears to go on in spite of the formation of fog.

A third process of fog-formation, namely, the descent of a cloud from above in the form of light drizzling rain, hardly calls for remark. In so far as it is subject to rules, they are the rules of clouds and rain and are therefore independent of surface conditions.

These various causes of fog-formation maybe considered with advantage in relation to the geographical distribution of fog. Statistics on this subject are not very satisfactory on account of the uncertainty of the distinction between fog and mist, but a good deal may be learned from the distribution of fog over the north Atlantic Ocean and its various coasts as shown in the Monthly Meteorological Charts of the north Atlantic issued by the Meteorological Office, and the Pilot charts of the North Atlantic of the United States Hydrographic Office. Coast fog, which is probably of the same nature as land fog, is most frequent in the winter months, whereas sea fog and ocean fog is most extensive and frequent in the spring and summer. By June the fog area has extended from the Great Banks over the ocean to the British Isles, in July it is most intense, and by August it has notably diminished, while in November, which is proverbially a foggy month on land, there is hardly any fog shown over the ocean.

The various meteorological aspects of fog and its incidence in London were the subject of reports to the Meteorological Council by Captain A. Carpenter and Mr R.G.K. Lempfert, based upon special observations made in the winters of 1901-1902 and 1902-1903 in order to examine the possibility of more precise forecasts of fog.

The study of the properties and behaviour of fog is especially important for large towns in consequence of the economic and hygienic results which follow the incidence of dense fogs. The fogs of London in

## particular have long been a subject of inquiry. It is difficult to get

trustworthy statistics on the subject in consequence of the vagueness of the practice as regards the classification of fog. For large towns there is great advantage in using a fog scale such as that given above, in which one deals only with the practical range of vision irrespective of the meteorological cause.

Accepting the classification which distinguishes between fog and haze or mist, but not between the two latter terms, as equivalent to specifying fog when the thickness amounts to the figure 2 or more on the fog scale, we are enabled to compare the frequency of fog in London by the comparison of the results at the London observing stations. The comparison was made by Mr Brodie in a paper read before the Royal Meteorological Society (_Quarterly Journal_, vol. 31, p. 15), and it appears therefrom that in recent years there has been a notable diminution of fog frequency, as indicated in the following table of the total number of days of fog in the years from 1871:--

+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+ | 1871.| 1872.| 1873.| 1874.| 1875.| 1876.| 1877.| 1878.| 1879.| 1880.| 1881.| 1882.| 1883.| 1884.| 1885.| 1886.| 1887.| 1888.| 1889.| +-------------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+ | 42 | 35 | 75 | 53 | 49 | 40 | 46 | 63 | 69 | 74 | 59 | 69 | 61 | 53 | 69 | 86 | 83 | 62 | 75 | +------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+ +------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+ | 1890.| 1891.| 1892.| 1893.| 1894.| 1895.| 1896.| 1897.| 1898.| 1899.| 1900.| 1901.| 1902.| 1903.| 1904.| 1905.| 1906.| 1907.| 1908.| +------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+ | 65 | 69 | 68 | 31 | 51 | 48 | 43 | 48 | 47 | 56 | 13 | 45 | 42 | 26 | 44 | 19 | 16 | 37 | 19 | +------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+------+

But from any statistics of the frequency occurrence of fog it must not be understood that the atmosphere of London is approaching that of the surrounding districts as regards transparency. Judged by the autographic records it is still almost opaque to sunshine strong enough to burn the card of the recorder during the winter months.

The bibliography of fog is very extensive. The titles referring to fog, mist and haze in the _Bibliography of Meteorology_ (