BOOK II
[THE NATURE OF AIR. THUNDER AND LIGHTNING]
[I.-XI. Prefatory to treatment of thunder and lightning, descriptive of the nature of the air, in which these phenomena occur.]
I. Divisions of physical science--astronomy, meteorology, geography. Cross divisions, _e.g._ earthquakes, belong to meteorology, being produced by air; so the earth, as a planet, belongs to Astronomy but its properties belong to Geography 51
II. Unity and composition in bodies. The analogy of the seen applies to the unseen. The atmosphere is possessed of unity (_unitas_) 52
III. Parts and material of bodies distinguished. In the human body blood is both 54
IV. The atmosphere is an integral part of the universe: has unity 54
V. The earth is both part and material of the universe. From it nourishment is supplied to the latter 55
VI. The atmosphere has unity--is not compact of atoms, otherwise it could not exert tension, which is one of its main features, with endless manifestations 55
VII. There is no vacuum in the air, as the analogy of water shows 57
VIII. The exertion of tension presupposes tensibility, just as motion does mobility. Its existence in air proved by the effects of air, which tosses about mountains, houses, walls, etc. The propagation of sight and sound proves the same 58
IX. Its tension is seen in raising water, as in the jet in the amphitheatre. Proofs from a ship upborne of water, a quoit flung from a height, sound heard through a wall 59
X. Varieties of density and temperature in the atmosphere: the central layer is coldest 60
XI. The lower parts are most subject to change. The cause of this is in part the earth, in part the sun, moon, and other stars. So much by way of preface to explain the nature of that atmosphere in which thunder and lightning occur 61
XII. _Lightning_, _thunder-bolt_, _thunder_. All agree that they occur in the clouds, but different explanations are given of their cause and relations. Anaxagoras connects them with the ether; Aristotle says they are due to exhalations of various kinds, from the earth, coming in contact with the clouds 62
XIII. The fire cannot be inherent in the clouds and fall from them. When it so comes it is forced 64
XIV. There is nothing inconsistent with this in the explanation given (I. xv.) of meteors. There may be an analogy with what is observed in cases of fire when isolated groups of houses take fire through gradual accumulation of heat 65
XV. Some (Stoics) think that spontaneous combustion takes place in the air 66
XVI. Difference between a flash of lightning and a bolt 66
XVII. Some explain the noise of thunder as due to hot meeting cold, as in the case of hot iron plunged into water 67
XVIII. Anaximander attributes the effects to air and explains all the phenomena by reference to it 67
XIX. Anaxagoras says it is the ether that acts on the lower atmosphere to produce them: it sends out fire 68
XX. Diogenes of Apollonia thinks that fire and air interact, producing one another, as may be observed in the various phenomena 68
XXI. Authorities discarded: independent explanation. A flash and a bolt are fire in some form: they differ only in degree 69
XXII. Analogy of fire on earth: it must apply above. Lightning due either to impact or friction. Hurricanes are a sufficient cause of the former 70
XXIII. Clouds and air may through friction also be a cause. The fires so produced are insubstantial and evanescent 71
XXIV. Fire by reason of its lightness levitates, just as water gravitates. But in the case of a bolt it is forced down, contrary to its nature, like a “weeping” tree 71
XXV. But it is said that wet clouds produce fire. How? 72
XXVI. There is no inconsistency in the combination in the same cloud of potential fire and water. A log burns at one end, exudes moisture at the other. An island on each of two occasions was thrown up by fire in the Aegean Sea, fire overcoming water. And clouds are, as a matter of fact, required for lightning: exceptions to this are only apparent 72
XXVII. Different kinds of thunder. The growling and the crashing, with their causes 75
XXVIII. In order to the sound of thunder, clouds of a particular shape must meet in a particular way. A bladder does not burst with a report if cut. A broad simultaneous blow over the whole cloud is necessary to an explosion 76
XXIX. The proper shape and the rupture of the cloud are necessary. Compare drums, etc. 77
XXX. According to some, clouds are not necessary to thunder: witness eruptions of Etna and the overthrow of Cambyses’ army, where particles of sand were the medium of the thunder and lightning. But in this case, too, a cloud was formed, it may be, a denser, and more solid than one composed of mere air, before the sound was emitted 77
XXXI. Strange effects of lightning 78
XXXII. Portents and events, their undoubted and widespread connection 79
XXXIII. Thunderbolts. Threefold division of the art of dealing with them 81
XXXIV. Mistaken views as to the relation of lightning to other presages. The former are of equal, not superior, value 82
XXXV. Fate cannot be changed by expiation and entreaty 83
XXXVI. “God is not a man” that he should change fate. What is the use, then, of rites? 84
XXXVII. Answer--Fate fixes some things only conditionally: the alternative issues are determined by the conduct, active or passive, of the worshipper 84
XXXVIII. This action of his is likewise a part of fate. The soothsayer, like the physician, is the minister of fate. Discussion of free will deferred 85
XXXIX. Three classes or kinds of thunderbolts, as judged by their indications, according to Caecina 86
XL. These are kinds of prognostications rather than of bolts. The different species of the latter are distinguished by their effects--boring, splitting, burning. Fine distinctions of Latin terms 87
XLI. A kind that stains or discolours. The Etruscan view of the three kinds of bolt according to _their_ division 88
XLII. The Etruscans knew what they were about in attributing certain motives and actions to Jupiter. Their theory was for the benefit of the ignorant mass of humanity 89
XLIII. “Which things are an allegory.” An example is set to earthly rulers to be merciful and consider well their judgments 90
XLIV. Jove does not change his missiles; but there are gradations in the offence to be punished. That is the lesson 91
XLV. By Jove the Etruscans meant, as we do, all that is greatest and best--Fate, Providence, Nature, the Universe 91
XLVI. He is the source of the thunder’s power, though he does not superintend each stroke. Why he spares the guilty is another affair, which will be discussed in another place 92
XLVII. An erroneous classification of thunderbolts according to time 92
XLVIII. It must be wrong, because the time is always limited. A better basis of treatment is that of Attalus. Place, time, person, etc., must all be looked into 93
XLIX. Caecina’s division, his names and their meanings 94
L. That of Attalus is much better, being based on the true signification 95
LI. The signification of some does not affect, of some does not reach, us 95
LII. The force of lightning as seen in different materials, and at different times in the same material (cf. xxxi.) 96
LIII. Poisonous effects: may be followed up afterwards. Panegyric on philosophy 97
LIV. Returns to Posidonius’ (Aristotle’s) opinion as to the cause of thunder, an explosion of air 98
LV. The collision of clouds may produce it. Air is the cause in this instance also. Shooting stars are associated with thunder, but this is the exception, not the rule 98
LVI. Heraclitus and Caecina think sheet lightning an intermittent incipient fire. Change in the pronunciation of the Latin word 100
LVII. Lightning is probably due to the air turning into fire through rarefaction of the clouds. It is naturally most frequent in summer. Sheet and forked lightning differ in degree, not in kind 100
LVIII. Reasons for rapidity of lightning and its obliquity 101
LIX. Every story should have a moral. Death cannot be prevented; why fear it? It is cowardly and silly. Death by lightning is rather an honour than otherwise. Besides, fear is futile 102