Chapter XV: Book II: The Nature of Air. Thunder and Lightning (1)

I

Every inquiry into the nature and constitution of the universe falls 1 into three divisions--astronomy, meteorology, and geography. The first investigates the nature of the heavenly bodies, the size and shape of the fires that ring-in the world. It inquires whether the heavens are solid, composed of strong rigid material, or woven of a fine thin stuff; whether they receive or impart motion; whether the heavenly bodies are beneath them or fixed in their texture; in what manner the sun maintains the succession of the seasons; whether he returns upon his track or not, and all the other questions of a similar character. The second division deals with what lies between heaven and earth, to 2 wit, clouds, rain, snow, and

Thunder that frights the heart of man:

in short, all that the atmosphere does or suffers. This subject is called meteorology (_sublimia_ = raised on high), because it deals with phenomena exalted above the low earth. The third part inquires about waters, lands, trees, crops, or to use a legal phrase, everything that is contained in the soil.

How comes it, you ask me, that you have put the question of 3 earthquakes in the division under which you are going to treat of thunder and lightning? For that is my plan. Well, the earthquake is due to air, and air is the atmosphere in violent motion. Now, though the air may enter the earth in order to produce earthquakes, the treatment of earthquakes does not fall under geography, but more properly belongs to meteorology, which deals with the sphere to which nature has assigned the atmosphere. I can tell you something that will sound stranger still: I must speak of the earth when dealing with the heavenly bodies. Why? you ask. For this reason: we discuss in 4 their own proper place, as part of geography, the properties of the earth, for example, whether it is broad, projecting unequally in a huge bulge to one side, or whether it all assumes the shape of a ball, gathering up its parts into a globe; whether it binds its waters or is itself bound by them; whether it is an animal or a lifeless mass without feeling, full of air no doubt, but not its own breath. These, and all other questions of the kind, as often as they crop up, will 5 be relegated to geography, and be placed in the lowest category. But when the question comes to be the situation of the earth, the part of the universe in which it has settled, its position with respect to the heavens and heavenly bodies, then the inquiry will take its place in the higher category,[34] and obtain higher rank so to speak.

[34] Viz. that of the heavenly bodies which constitute the subject
matter of astronomy.

II

Having described the three divisions into which all the material of 1 nature falls, I must add a few general remarks on the subject. And this must be premised, that the atmosphere belongs to the class of bodies that possess unity. What exactly this means, and why it must be laid down as an axiom, will appear if I go back a little, and entering more fully into the subject, tell you that certain bodies are continuous, and certain formed, by a union of different elements.[35] Continuity may be defined as unbroken union of parts one with another. Unity 2 is continuity without a break; it is the contact of two bodies joined to one another. There can be no shadow of doubt that of the bodies around us which we see and handle, and which are either perceived or perceive, certain are composite. They are so either through nexus or 3 through mere accumulation; take as illustrations a rope, corn, a ship. Again, there are bodies that are not composite, as a tree, a stone. You must, therefore, grant that likewise among the objects that elude sense, and are grasped only by thought, some are possessed of unity[36] [while some arise from junction of parts]. See how careful I am of your susceptibilities. If I had chosen to employ the jargon of philosophy, 4 I might have got out of the difficulty by merely saying “united bodies.” You must, in turn, be duly grateful for this concession to your weakness! What am I driving at? This: if at any time I speak of “unity” in this connection, bear in mind that it is not used of number, but has reference to the composition of a body that coheres through no external aid, but by its own unity. To this category the atmosphere belongs.

[35] This difficult passage, according to Gercke’s text, runs:
You will understand the meaning of this, and the necessity for my
axiomatic position if I take up the argument a little farther back,
and say that there is one kind of body possessing unity, another that
is continuous, and another that is formed by junction. For junction
is the contact of two bodies joined one to another, continuity is the
uninterrupted joining of parts one to another, unity is continuity
without junction (_i.e._ without a break).

[36] That is, are not composite.

III

The universe embraces all the objects that fall, or that can fall, 1 under our cognisance. Of these some are its parts, the remaining ones must form its material. Nature, just like every manual art everywhere, requires material. Let me make this a little plainer. In ourselves 2 the parts are hand, bones, sinews, eyes; the material is the sap of the digested food, which will be distributed for the nourishment of the parts. Again, blood is in a certain sense a part of us, but still it is material as well. For it goes to form other parts, and, none the less, it is among the parts that go to make up the whole body.

IV

So the atmosphere is a part, a most necessary one, of the world. 1 This it is that joins heaven and earth, separating highest and lowest in such a way as yet to unite them. It separates by coming in between, it unites by rendering possible communication between the two. It transmits to the higher regions what it receives from the earth; and again, it transfuses terrestrial objects with the influences of the heavenly bodies. I call it a part of the world in the same sense as animals and trees are parts. The whole class of animals and trees forms 2 part of the universe, since it has to be taken in to make up the whole, and without it the universe is not complete. A single animal or tree is a quasi-part: though it is lost, that from which it is lost is still entire. Now the atmosphere, as I have been saying, adheres both to sky and earth. In both it is inborn. Whatever is an inborn part of anything else possesses unity, for without unity nothing can be born.

V

The earth is at once part and material of the world. You are not, I 1 think, more likely to ask why it is a part than why the sky is a part. The one is just as essential as the other to the existence of the whole, which they go to make up, and from which [from the one no less than from the other][37] sustenance is provided for all animals and crops and stars. From the earth all the strength of every man, all 2 the energy of the world with its ceaseless demands, are supplied. Hence proceeds the force that, by day and by night, sustains in their labours so many stars, so active and so eager, and that provides their food. The universal nature derives from this source what suffices for its nourishment. The world has appropriated all that it requires throughout eternity. To adopt a tiny illustration of a great subject: eggs enclose within them as much moisture as they require for the completion of the creature that is to be hatched.

[37] The words in brackets are in all probability spurious, the
addition of some commentator. The whole passage is very uncertain.

VI

The atmosphere is in unbroken contact with the earth, in such close 1 juxtaposition that it must always occupy the space that she has just quitted. It is a part, as I have said, of the universe. At the same time it receives all that the earth sends forth for the nourishment of the heavenly bodies; so that, of course, it should be understood in this connection as material rather than part. It is these earthy elements that cause its fickleness and constant turmoil. Some authorities believe the atmosphere to be composed of separate bodies as dust is, but they are sadly in error. For there can never be internal effort in a body held together in any other way than by unity,[38] 2 since the elements must be in agreement in order to contribute their united strength toward the tension. Now, the atmosphere, if assumed to be cut up into atoms, must be dispersed. Scattered elements cannot hold together as one body. But, as a matter of fact, the tension of the atmosphere is proved by inflated objects that will not yield to a blow. It is proved, too, by weights carried up to a great height merely by the support of the wind. It is proved by the sound of voices sinking or swelling, according to the stirring (= vibration) of the air. For what is voice save tension of the air moulded by a 3 stroke of the tongue so as to become audible? What is all running and motion? Are they not the effects of tense air? This it is that imparts strength to the sinews, and endows the runner with his speed. When, being violently stirred, it has twisted itself into an eddy, it uproots trees and woods, carries aloft and shatters whole buildings. When the sea lies all peaceful, the air raises it in waves. Or, to descend to 4 less violent manifestations, what song can be sung without tension of breath? Or, take horns and trumpets, or those organs that by means of hydraulic pressure can produce a greater volume of sound than the mouth is capable of doing: is it not through atmospheric tension that they display their functions? Or, let us note what an enormous force is 5 exerted in secret by quite tiny seeds, whose smallness has allowed them to find a lodgment in the clefts of stones. Their slender diminutive roots gather strength enough to dislodge huge boulders, split statues, and cleave crags and rocks. And to what is this due but air tension, 6 without which there is no strength, over which no strength can prevail? The unity of the atmosphere may, in fact, be inferred from the mere coherence of our bodies. What else is it that holds them together save air? What else is it by which the soul is stirred (literally, moved)?[39] What constitutes that motion if it be not tension? What 7 tension can there be except from unity? What unity could there be unless it were in the air? What else, too, brings forth from the earth its fruits and slender grain, and sets erect the verdant trees, and stretches out their branches, or sets them on high, but the tension and unity of air?

[38] Or, except in a body of uniform texture.

[39] Nisard translates, What imparts movement, in man, to the vital
principle?

VII

Some writers believe that the air is rent and separated into small 1 parts with void spaces, as they suppose, between. They consider the easy flight of birds through it a proof that it has not a compact body, but has large empty spaces: fowls, great and small, pass through it without difficulty. But this is a mistake. For water also affords the same easy motion, and there is no doubt of its unity. When it 2 receives bodies, it always retreats in the direction opposite to them. This the Stoics call displacement, in Greek it is peristasis,[40] which takes place in air just as it does in water. For it literally stands round every body by which it is pressed. There is no need to assume an admixture of vacuum with the element. But more of this another time.

[40] περίστασις = a standing around. The Latin equivalent in the text
is _circumstantia_, rendered “displacement.”

VIII

From what has been said it must be inferred that in nature there 1 exists a principle of activity of enormous force. For there is nothing that does not become more active through tension; and it is no less true, nothing will be found capable of tension from another body unless it have in itself capacity of tension.[41] In the same way we say that nothing could be moved by another body without possessing the quality of mobility in itself. But what element can be conceived more likely to possess tension in itself than air? Will any one deny that it can be subject to that force after seeing how it tosses about the earth 2 with its mountains, houses, and walls and towers, and great cities with their inhabitants, seas, and whole coast-lines? The tension of air is proved, too, by its velocity and expansion. Illustrations of these properties are common: in an instant the eye extends its sight over many miles; a single voice resounds at the same moment through whole cities; light does not creep forth little by little, but is shed simultaneously over the whole world.

[41] The reading at several points is so uncertain that one cannot
be at all sure of the meaning. Probably the whole passage is very
corrupt. So far as the main theme is concerned, the argument seems to
be, As mobility is a presupposition of motion, so tensibility is a
necessary condition of actual tension produced in a body by another
body. One is tempted to employ “elasticity,” but the term contains
implications with which the author was apparently unfamiliar.

IX

Again, how could water be subject to tension without the aid of 1 air? You entertain no doubt, I suppose, that the jet of water in the amphitheatre, which is thrown from the centre of the arena to the highest pinnacle, is accompanied by tension of the water? And yet neither hand[42] nor any other engine can send or force water more effectively than air. It lends itself readily to the influence of the 2 air, by the compelling force of which within the pipe it is raised. Its nature is to flow down, but under pressure it mounts and accomplishes great results contrary to its nature. Yes, and do not heavily laden vessels also prove that it is the resistance of air, not of water, that prevents their sinking? The water of itself would give way, and would be unable to bear up the burthens, were it not itself upborne. So, too, a quoit thrown from a height into a pond does not fall straight 3 in, but recoils, and that merely because the air bears it back. In what way, again, could the sound of a voice be transmitted through the thick barrier of a wall unless the solid masonry contained some air to receive and transmit the sound from without? The tension of the air, of course, affects not only what is exposed, but what is concealed and enclosed as well. This is easy for it to do, since it is never 4 divided, but maintains an unbroken continuity even through the centre of objects by which it appears to be parted. The interposition of walls and high mountains renders it impassable by us, but is no obstacle to itself. The air is there all the same,[43] but a portion is enclosed and we cannot follow it through; that’s all.

[42] A conjecture widely adopted gives “crane.”

[43] The general sense is clear, but the particular text is uncertain.

X

Thus the air passes through the middle of an obstacle by which it is 1 apparently divided. It not merely surrounds and encircles all objects, but permeates them likewise. It is shed abroad from the bright ether on high down to the very earth. It is nimbler and rarer and more exalted than the earth, and no less so than the waters of earth; but, on the contrary, it is thicker and heavier than the ether, and is naturally cold and dark, its light and heat coming from without. It is not of the same specific quality in every region, but borrows its qualities from its surroundings. The highest part of it is extremely dry and 2 hot, and so, very rare also, from the proximity of the eternal fires, the endless motions of the stars, and the constant revolution of the heavens. But the lowest portion next the earth is dense and dark, because it forms a receptacle for the exhalations of the earth. The intermediate portion, in dryness and rarity, runs to neither extreme as compared with the highest and lowest strata, but is colder than either. The reason is this: The higher parts are affected by the heat of the 3 heavenly bodies that are close by; and again the lower parts are warmed in the first place by the earth’s breath which is charged with heat, while in addition the sun’s rays are reflected from the ground, and as far as the reflection extends it renders the atmosphere kindlier and more genial. Besides, the temperature of the lower air is raised by the warm breath of all animals, trees, and crops, whose life is dependent on heat. Add to this also fires on the earth, not merely the 4 artificial ones about which we know, but also those concealed beneath it, some of which have ere this broken out, and myriads of which are blazing away in the hidden depths incessantly. Add, too, that all the fertile parts of the earth have some degree of heat which is exhaled into the air: heat is a condition of generation, the frigid is sterile. So, then, the middle portion of the atmosphere being remote from all these influences abides in its native cold: for air is by nature chilly.

XI

Such being the divisions of the atmosphere, I may observe that in 1 its lowest layer it is most variable, unstable, and changeful. It is near the earth that the air is, so to speak, most enterprising and most long-suffering, as it tosses or is tossed. But withal, it is not all affected in the same way, but at different times at different points its different parts are in unrest and turmoil. The reasons of the changefulness and inconstancy are in part derived from the earth: her position turning hither and thither is a potent factor in determining the quality of the atmosphere. Other reasons are due to the heavenly bodies, chiefly the sun, whose course directs the year, whose solstices determine winter and summer. Next in importance is the moon’s influence. But even the other stars produce an effect alike on 2 the earth and on the air that rests upon the face of the earth. Their rising or their corresponding setting and their disturbances cause now cold, now rain, now other damage such as earth is subject to.

It was necessary for me to make these preliminary remarks before going on to speak of thunder and thunderbolts and lightnings. For as these phenomena occur in the atmosphere, I had to explain the nature of the latter, that it might more readily appear what active or passive capacities it possessed.

XII

There are, I have just said, three phenomena--lightnings, 1 thunderbolts, thunderings: the last is simultaneous in occurrence with the others, but its sound reaches us subsequently. Lightning (_i.e._ sheet) merely reveals fire, the thunderbolt (forked lightning) actually despatches it on its mission. The former is, so to speak, a threatening and feint without a blow, the latter a stroke and a blow. There are some of the facts connected with the phenomena of thunder and lightning on which there is general agreement, others on which there is much diversity of opinion. For example, there is agreement that they 2 occur in the clouds and issue from the clouds; further, it is agreed that lightning of both kinds is either composed of fire or at any rate presents the appearance of fire. But to pass on to the points which are disputed--some authorities believe that the fire is actually resident in the clouds, some that it is merely produced for the occasion, and that it does not exist until it issues out. But yet there is no agreement as to what brings out the fire. One explains it as due to 3 light. Again, a certain author says that the sun’s rays accumulate through recurrent intersection, and kindle the fire. Anaxagoras asserts that it is distilled from the ether, that from such heat in the sky many sparks fall which the clouds enclose and retain for a long time.

Aristotle supposes that the fire does not gather in the clouds any long time previously, but rather that it bursts out at the same instant as it is formed. His opinion runs thus: Two elements of the world, 4 land and water, lie in its lower part; each exhales its peculiar emanation. The vapour of earth is dry, resembling smoke, and produces wind, thunder, and lightning; the breath of water, on the other hand, is moist, and produces rain and snow. But that dry vapour from the earth, to which [as mentioned] winds owe their origin, on account of its accumulation in large masses, is subject to violent lateral pressure when it is condensed for the formation of clouds. Thereupon it strikes the adjacent clouds over a larger surface, and the blow 5 reverberates loudly [in thunder]. The effect is analogous to that produced by the crackling of flame from the moisture contained in green unseasoned firewood. In this case the air enclosed in the wood has some moisture in it, and when it accumulates it bursts out in the flame. So likewise the air which, as I said a little ago, is driven out through a collision of two clouds, cannot burst or leap out without noise. The sound varies according to the variety of impact in the clouds; the 6 larger cavity in some clouds, the smaller in others account for the variety. That air violently driven out is fire, which is called sheet lightning when it forms a fitful flame of no great violence. We see the flash before we can hear the sound: eyesight is swifter than hearing, and far outstrips it.

XIII

The mistakenness of the opinion that the fire is stored up in the 1 clouds may be inferred from many considerations. For example, if the fire merely falls from the sky, why does it not do so every day from the glowing mass that is constantly up there? Then, again, the theory gives no explanation of the downward course of the fire, an element which naturally rises. Fires on earth from which embers fall belong to a different category; the embers possess a certain amount of weight, which carries them down. Fire cannot descend in the same way, but must be forced or conducted down. Nothing analogous to a terrestrial fire 2 can take place in that pure ethereal fire which contains nothing that can carry it down to earth. Otherwise, if any portion of it fall down, the whole is endangered; for anything susceptible of gradual diminution piecemeal may evidently also fall in a mass. Besides, if an element whose lightness habitually prevents its fall contain any weight in its hidden depths, how could it maintain itself in the place whence it fell? But, it is urged, are not certain forms of fire wont to descend into the lower parts of air very much like these bolts of lightning that we are investigating? Admitted. Only they are conveyed, they do 3 not proceed of themselves. Some force not resident in the ether carries them down. For in the ether no violent compulsion, no breach, no interruption of the wonted continuity, can occur. It preserves a fixed succession; its fire cleansed of impurity claims the upper regions as its own, and performs its functions in preservation of the universe with beautiful precision. It cannot leave its place, no, nor even be thrust from it by external force, because no disturbing body can find lodgment in ether. Its fixed and ordered composition renders conflict impossible.

XIV

Some of your friends the philosophers, a critic may say to me, in 1 giving an explanation of shooting stars have told us that some parts of the atmosphere contract fire which is drawn from these same higher regions, and that the fires are kindled by the glow of the ether. Yes, but I reply that it makes all the difference whether the fire is alleged to fall from the ether, which is incompatible with its nature; or whether it is asserted that from its fierce glow the heat leaps the boundary between it and the lower regions, firing them by its power. For on the latter assumption, the fire does not fall from the upper region, which is impossible, but is kindled in the lower. Surely, too, when a widely spread conflagration occurs in one of our cities, we 2 see detached blocks which have for long been heated by the fire from a distance at last catch fire of themselves. So in the upper atmosphere, which is endowed with the power of drawing fire, in all probability there are cases of ignition from the heat of the superposed ether. In nature there is never a sudden transition from one element to a totally different one. Hence there must be some congruity between lowest ether and highest atmosphere; conversely highest atmosphere cannot be wholly dissimilar to lowest ether. On the confines the two elements pass so imperceptibly into one another that at a particular point there might well be doubt whether one is in atmosphere or in ether.

XV

Some of the Stoics believe that air, being interchangeable with other elements such as fire and water, does not derive from without a fresh cause of fire; it kindles itself by its internal motion. Then in dissipating masses of thick, compact clouds it necessarily emits a loud noise from the bursting of such large bodies. Besides, the very conflict of the resisting clouds contributes to the energy of the fire. In the same way the hand contributes to the cutting power of an instrument, but the actual cutting is done by the steel.

XVI

Let me now explain the difference between the flash and the bolt of lightning which you naturally wish to know. The flash is the fire widely spread out, the bolt is the condensed fire hurled with violence. Let me use a homely illustration. We sometimes join our two hands in order to take up water in them; then we squeeze our palms together and squirt out the water like a syringe. Imagine something like this to take place in the clouds. When they are compressed the restricted space drives out the air between them, setting it on fire at the same time, and hurling it forth like a cannon ball. The missiles from our balistae[1] and scorpions[44] give forth a loud noise as they are hurled.

[44] The ancient counterparts of cannon.

XVII

A certain number of writers are of opinion that the air of itself emits a report as it traverses the cold and moist regions. Iron, they point out, when heated cannot be dipped in moisture without noise. A mass of heated metal when plunged in water causes a loud sputtering as it is cooled; so, according to Anaximenes, air meeting cloud produces peals of thunder; then as it rushes struggling through the obstructions that bar its way it kindles the flame of lightning merely by its escape.

XVIII

Anaximander refers all the phenomena of thunder to air. Peals of thunder are, he says, the sounds of blows on a cloud. He explains the inequality of the peals by the inequality of the blows. To the question, why it thunders in a clear sky also, he answers that even in absence of cloud the atmosphere is shaken and rent by the bursting forth of air. But why is there thunder sometimes and yet no lightning? The rarity and feebleness of the air render it incapable of producing flame, while yet sufficient to produce sound. Lightning, according to him, then, is really a disturbance where the atmosphere is merely parted and rushes hither and thither, displaying a faint fire that will not issue from its place. As for the thunderbolt, it is the career of the more active and denser air.

XIX

Anaxagoras says all the phenomena correspond to the descent of some 1 force from the ether to the lower regions. So when the fire encounters cold clouds it emits a sound; when it cleaves them there is a flash; less violence in the fires produces lightning, greater, thunderbolts. 2

XX

Diogenes of Apollonia asserts that thunder arises in some cases from 1 fire, in some from air. Fire precedes those it produces, to herald them. Those that are attended with rattling noise, but without flash, are produced by air. Either sound or flash, I grant, can and sometimes does occur without the other. Still, their powers are not distinct, each may be produced by each. For will any one say that air borne with great violence, when it can produce sound, will not also produce fire? Will not every one grant, too, that fire as well as air may 2 sometimes burst the clouds without darting from them, for example, if it has burst through a few of the clouds, but is buried beneath an accumulation of them? So fire will pass into air, and lose its shining appearance in cutting through some cloudy obstacles and kindling what is within. Add now another inevitable result--the rush of the thunderbolt sends out blasts of air and drives them before it, and raises a wind behind it through the great extent of its impact on the atmosphere. Thus, through the vibration caused by the wind which the fire drives in front of it, all objects quiver before they are actually struck by the bolt of lightning.

XXI

We must now dismiss our tutors and try to walk alone as we pass on 1 from what is admitted to what is debatable in this subject. What is to be classed as admitted? It is admitted that the thunderbolt is fire of some kind; similarly with the lightning flash, which is simply flame ready to become a bolt if it had more strength. The difference between the two is not in character but in force. The fiery nature of the bolt is proved by its heat. Apart from that, its effects prove it, for it has often been the cause of great conflagrations. Forests and 2 portions of cities have been burnt to ashes by it. Even objects that are not struck are yet seen to be scorched, some are discoloured as if by smoky grime. Then, again, everything that lightning strikes has the smell of sulphur. And so it is beyond dispute that both phenomena are a form of fire, and that they differ merely in their method of movement. A flash is a bolt that has not strength to carry it down to the 3 earth. And conversely you may say that the bolt is a flash that has been conveyed right down to the ground. It is not for the purpose of refinement of terms that I deal at some length with them, but in order to prove the phenomena related and of the same category and character. A bolt is something more than a flash. Inverting the statement, a flash is all but a bolt.

XXII

Now that it is agreed that the two things are both fire, let us see 1 how fire arises on earth, for no doubt the same method prevails aloft. There are two common methods of producing fire--one by striking it out, as, for example, from a stone; the other by the more tedious method of friction, as when two pieces of wood are rubbed together for some time. It is, of course, not every kind of substance that gives the desired result; you must choose one suitable for giving out fire, for example, laurel, ivy, and other trees familiar to shepherds for this purpose. Probably, therefore, clouds may in the same way emit fire either from a blow or from friction. Consider for a moment the force with which squalls rush forth, the impetuous eddying revolution of 2 the whirlwind. Anything that encounters a missile from an engine of war is scattered and removed and driven far from its position. What wonder, then, that such violence in the wind extracts fire either from some external object or merely from itself? You can readily see what a glow all neighbouring bodies grazed by its passage must receive. But the force of storms cannot for a moment be compared with the energy of the heavenly bodies, whose immense power is beyond question.

XXIII

Perchance, too, when the wind only blows softly and exerts no great 1 force, the clouds, wafted against each other, will emit fire strong enough to show a gleam, though not to issue from them. Less force is required for lightning than for the thunderbolt. We found above what a glow the friction of certain woods caused. Now when the air, which is interchangeable with fire, [has been changed in full force into fire 2 and][45] undergoes friction, it is credible and even probable that fire is struck out, but of an evanescent and transitory character, as it arises from no solid material and has no fuel in which it can lodge. It therefore quickly passes; its duration is no longer than its route and course; it has nothing to support it when hurled forth into space.

[45] These words seem of more than doubtful genuineness.

XXIV

But how, you ask me, when you philosophers say that it is the nature 1 of fire to rise, does the bolt seek the earth? Perhaps what you said about fire is not true? It seems to take its course down as well as up.

Both my statements, I reply, may be true. Fire naturally does rise and mounts if nothing prevents it, just as water naturally gravitates downwards. But water if affected by a force which drives it uphill is pressed up in the direction from which it was precipitated in rain. In like manner the same force as launched the bolt from the cloud causes it to fall to the ground. Something of the same kind happens to these 2 celestial fires as to trees when bent. The topmost branches if slender may be dragged down so as to touch the ground; but when you let them go, they rebound to their original position. You must not regard the condition which an object involuntarily assumes as characteristic of it. If you allow fire to go where it will, it will return to the sky, the abode of all the lightest bodies. But when there is anything to carry it down and divert it from its natural course, that is not a mark of its disposition but a token of its subjection.

XXV

You and your friends say, an objector interposes, that clouds emit fire through mutual friction when they are moist, indeed wet. How can such clouds produce fire, which is no more likely to be generated by a cloud than by pure water?

XXVI

Well, first of all, the fire which is thus produced is, as it is 1 found in the clouds, not water, but thick air, adapted for the generating of water; it is not yet changed into it, but is already inclined toward, and ready for, the change. There is no ground for supposing that water is first gathered in the clouds and afterwards shed from them. It falls simultaneously with its formation. But in the second place, though I grant that the cloud is moist and charged with fully formed water, still there is nothing to prevent fire being drawn from what is moist, yes--and what will surprise you more to learn--out of pure moisture. Some authorities have actually affirmed 2 that nothing can be converted into fire without a prior change into water. A cloud, then, without prejudice to the water it may contain, may emit fire at some part of it, just as often one end of a log is blazing while the other exudes moisture. I do not deny that fire and water are opposing elements and that the one destroys the other. But where the fire is stronger than the water it wins the day. On the other hand, where there is a superabundant supply of moisture, then fire is powerless. That is why green wood won’t burn. The result depends, therefore, on the quantity of water present. If it is small, no effectual resistance is offered, the fire is not prevented. Why, 3 according to Posidonius’ account, when an island rose in the Aegean Sea long ago in our forefathers’ days, the sea was lashed into foam for a long time previously and sent up smoke from its depths. At last fire was emitted, not continuously, but in flames shooting out at intervals, after the fashion of thunderbolts, just as often as the fervent heat of what lay below had overcome the weight of water above it. By and by boulders were thrown up and rocks, part of them still unimpaired, 4 which the air had thrust out before their calcination, part of them corroded by the fire and changed to light pumice; at last the cone of a blasted mountain issued from the waves. Subsequently, there was an addition to its height, and the rock grew in extent into an island. The same thing happened within our own recollection during the second consulship of Valerius Asiaticus.

Why have I narrated these incidents? My purpose was to make it 5 evident that neither is fire necessarily extinguished by having the whole sea poured over it, nor its violence prevented from bursting out by the weight of huge waves. Asclepiodotus, a pupil of Posidonius, has left it on record that the height to which the fire mounted, after overcoming the resistance of the waves, was a hundred fathoms. Now, if such a huge mass of water was unable to overcome the force of the flames that rose from its depths, how much less can the thin, dewy moisture in the clouds extinguish fire in the atmosphere? In short, the 6 moisture of the clouds is so far from presenting any obstacle to the formation of fire that lightning is never seen to flash except when the sky threatens rain. A clear sky has no bolts to hurl. No terror of that sort proceeds from a bright day, nor for the matter of that from a night that is not enveloped in cloud. But what! I hear some one say. Does it not sometimes lighten in a calm night when the stars are visible? It does, but you must remember that there are clouds all the 7 same in that quarter whence issues the flash; only, the earth’s hump does not allow them to be seen by us. Add, too, what is quite possible, that low clouds near the earth may produce fire through friction. This fire when forced up to the upper regions becomes visible in the clear bright part of the sky, but none the less its place of origin was in the dark vicinity of earth.

XXVII

Some writers have distinguished different kinds of thunder, saying 1 there was one kind with a deep growl like that which precedes an earthquake, when the wind moans and tries to burst its prison walls, Let me tell you how they suppose this kind of thunder to arise. When the clouds have enclosed air, it rolls through their cavernous depths and emits a hoarse, regular, continuous sound like bellowing. So also when that quarter of the heavens is charged with moisture, its exit is prevented until the thunder begins. Therefore, thunder of this kind 2 is a sure sign that rain is to follow. There is another kind, which is sharp, and it might be described more accurately as a crackling than as a regular sound; it resembles the report one hears when a bladder is burst over some one’s head. Such thunder is the result of the breaking up of a densely massed cloud and the release of the air by which it was inflated. This is appropriately named a peal, sudden and violent. When it occurs, people collapse and are sometimes literally frightened to death by it; others retain life, but are dazed and completely lose their wits: we call them thunder-struck, for that sound in the heavens has quite unhinged their minds. This sound may also be produced by 3 the atmosphere shut up in a hollow cloud being rarefied, merely through motion, and expanded. By and by in seeking more room for itself it resounds against the walls that envelop it. In fact, is it not just similar to the applause given out by the clapping of the hands? only, when the clouds collide, the sounds may be expected to correspond in volume to the greatness of the encountering bodies.

XXVIII

But clouds, says some one, are seen striking upon mountains. without 1 causing any sound. How is that consistent with your theory? Well, in the first place, a sound is not caused by any and every method of cloud collision, but only when there is an arrangement of their position suitable for producing a sound. Striking the backs of the hands does not produce clapping, but the contact of palm with palm does. It makes a great difference, too, whether the clouds that strike are hollow, or flat and extended. In the second place, the clouds must not merely drift, as against a mountain, but be driven with great tempestuous violence. Besides, a mountain does not cut through a cloud, it merely 2 disperses it by displacing the successive front layers of it. Even a bladder does not give a report irrespectively of the method in which it emits the air in it; it depends on the way in which the air escapes. If the bladder is cut with a knife, the air is emitted without the ear perceiving it. It must be burst, not cut, in order to give a report. The same, I assert, holds in regard to the clouds: they emit no peal unless broken up with great violence. Besides, clouds driven against a mountain are not broken up, but merely pour round certain parts of 3 the mountain, tree branches, shrubs, and rough projecting boulders. They are rent thereby, and emit by numerous exits whatever air they may contain; but there is no rattle unless the air all burst out at once. In proof of this, bear in mind that the wind blowing through a tree, 4 which cuts it, hisses but does not roar. A broad blow, so to speak, that dissipates the whole mass at once, is required in order to the emission of a sound such as is heard when there is thunder.

XXIX

Moreover, the atmosphere is by constitution adapted to the transmission of sound.[46] Of necessity this is so, since sound is nothing but an impact of the atmosphere. The clouds that [as indicated] are completely rent must therefore be hollow and taut. One sees how much more resonant empty vessels are than full, and distended ones than slack. So this accounts for the sound of tambourines and cymbals; the former resound because the blow upon the air is resisted at the farther side; the latter are beaten against the air directly, but unless there were a cavity in the instrument it would not tinkle.

[46] The specific word _vox_ = voice is used in the text.

XXX

Some authors, including Asclepiodotus, are convinced that thunder 1 and lightning may also be produced by the collision of certain solid bodies. Once Etna was in violent eruption and cast up a huge quantity of burning sand. The daylight was veiled with the cloud of dust, and sudden night terrified the world. On that occasion, they allege, there was much thunder and lightning, produced, they maintain, by the concourse of dry bodies, not of clouds: with such a glow in the firmament there probably were no clouds at all. Cambyses once sent an army to the temple of Jupiter Ammon in the desert. The sand raised by 2 the south wind fell on it like snowflakes, first covering and finally overwhelming it. Probably on that occasion also there was thunder and lightning, caused by the mutual friction of the particles of sand. Such a view is not inconsistent with my contention above. I have said that 3 the earth’s exhalations contain bodies of two kinds, dry and moist, portions of which roam through the whole expanse of the atmosphere. So if any heavy element be introduced, it makes a cloud thicker and more solid than if its texture were of pure air exclusively. Such a [solid] cloud may burst with a loud report. The elements I have 4 mentioned, whether they have charged the atmosphere with moist fires or with earth-sweeping winds, must produce a cloud before they produce a report. Dry elements no less than moist may make up a cloud. For cloud, as we have already said, is just a condensation of thick air.

XXXI

But further, if you will but open your eyes to them, there are 1 marvellous effects in lightning that leave no doubt that a subtle divine power is inherent in it. For example, coins are fused while the purse containing them is uninjured and intact. A sword is melted while the sheath remains. The iron point is fused in a javelin, but the wooden shaft suffers no damage. The jar is smashed and the wine frozen, but the stiffness does not last for more than three days. There are other no less notable effects of lightning. The head of 2 man or other animal struck by it always points in the direction whence the lightning issued: the twigs of all trees that are struck rise straight up in the direction of the lightning. Let me add, too, when venomous serpents or other animals whose bite is fatal are struck with lightning, all the poison disappears. How, you say, can I tell that? In the dead bodies of poisonous animals worms are not produced. But when struck with lightning they breed worms within a few days.

XXXII

Lightning portends the future, too. Nor do the signs it gives refer 1 to only one or two events. Often a complete series of fate’s succeeding decrees is intimated, with proof, too, plain to demonstration, far more distinct than if it were recorded in writing. There are differences of interpretation, however, between our countrymen and the Tuscans, the latter of whom possess consummate skill in the explanation of the meaning of lightning. We think that because clouds collide, therefore 2 lightning is emitted; they hold that clouds collide in order that lightning may be emitted. They refer everything to the will of God: therefore they are strong in their conviction that lightning does not give an indication of the future because it has occurred, but occurs because it is meant to give this indication. Whether the indication is its purpose or its consequence makes no difference in the method of its occurrence. How, then, do they give indication unless they are sent by God? Just in the same way as birds give favourable or unfavourable 3 omens, though they are not moved on their flight for the express purpose of meeting us. God moves them too, it is urged. You imagine He has so little to do that He can attend to trifles of this sort, if you will have Him arrange visions for one, entrails of victims for another.

Nevertheless, all those things are managed by Divine agency, not, 4 however, in the sense that the wings of birds are immediately directed by God, or the bowels of cattle arranged by Him in certain forms under the priest’s axe. It is in far other way that the roll of fate is unfolded; it sends ahead in all directions intimations of what is to follow, which are in part familiar, in part unknown to us. Everything that happens is a sign of something that is going to happen: mere chance occurrences uncontrolled by any rational principle do not admit of the application of divination. An event that belongs to a 5 series thereby becomes capable of being predicted. But why, then, is the honour conferred upon the eagle of giving omens concerning great events? or a similar function assigned to the raven and a very few other birds, while all the rest give no presage by their notes? The reason simply is that some departments have not yet been brought within the sphere of the art of augury, while some are incapable of ever being brought within it, because our acquaintance with them is too slight.

As a matter of fact, there is no living creature whose movement or 6 meeting with us does not foretell something. Of course, only some, not all, can be observed. The omen lies in the observation. So it concerns the person who directs his attention to it. But other things as well concern him, though they pass unheeded. For instance, the Chaldaeans confined their observation to the five great planets. But do you suppose that the influence of so many thousands of other bright stars is naught? The essential error of those who pretend to skill in 7 casting the horoscope lies in limiting our destinies to the influence of a few of the stars, while all that float above us in the heavens claim some share in us. Perchance the lower stars exert their force on us more directly; and[47] the same may be true of the stars that by reason of their more frequent movements turn their view upon man in a different way from that in which it is turned upon other living creatures. But even those stars that are either stationary or, from their velocity being the same as that of the world as a whole, seem to be so, are not without sway and dominion over us. Add one other 8 consideration and you have the subject set out with due arrangement of its parts:[48] it is not more easy to ascertain what the power of the stars is than justifiable to doubt that they possess such power.

[47] Or, Turn their view upon man no less than on the other living
creatures now from one point, now from another, _i.e._ under more
varied aspects. The passage is doubtful. The general sense is plain:
nearness, frequency of appearance, and variety of aspect severally
are or may be special factors in determining a star’s influence on
the fate of man.

[48] The text is corrupt and the sense more or less conjectural.
Ruhkopf suggests that the words may have been transferred from some
other passage to this. One would be inclined to suspect that _adjice_
= add, instead of _aspice_ = see, regard, is the correct word at the
beginning of the sentence.

XXXIII

To return now to lightning: the art relating to it falls into three divisions--its observation, its interpretation, its deprecation. The first has regard to the category in which it should be placed, the second to divination, the third to the propitiation of the gods, whose blessings we ought to ask and whose threats we must avert by prayer. We must ask them to fulfil their promises, pray them to remit their threats.

XXXIV