Epicurus to Pythocles, wishing he may do well.

    "Cleon has brought me your letter, in which you continue to evince towards me an affection worthy of the friendship which I have for you. You devote all your care, you tell me, to engraving in your memory those ideas which contribute to the happiness of life; and you entreat me at the same time to send you a simple abridgment and abstract of my ideas on the heavenly phænomena, in order that you may without difficulty preserve the recollection of them. For, say you, what I have written on this subject in my other works is difficult to recollect, even with continual study.

    "I willingly yield to your desire, and I have good hope, that in fulfilling what you ask, I shall be useful too to many others, especially to those who are as yet novices in the real knowledge of nature, and to those to whom the perplexities and the ordinary affairs of life leave but little leisure. Be careful then to seize on those precepts thoroughly, engrave them deeply in your memory, and meditate on them with the abridgment addressed to Herodotus, which I also send you.

    "Know then, that it is with the knowledge of the heavenly phænomena, both with those which are spoken of in contact with one another, and of those which have a spontaneous existence, as with every other science; it has no other aim but that freedom from anxiety, and that calmness which is derived from a firm belief.

    "It is not good to desire what is impossible, and to endeavor to enunciate a uniform theory about everything; accordingly, we ought not here to adopt the method, which we have followed in our researches into ethics, or in the solution of problems of natural philosophy. We there said, for instance, that there are other things, except bodies and the void, and that the atoms are the principles of things, and so the rest. In a word, we gave a precise and simple explanation for every fact, conformable to appearances.

    "We cannot act in the same way with respect to the heavenly phænomena; these productions may depend upon several different causes, and we may give many different explanations on this subject, equally agreeing with the impression of the senses. Besides, it is not here a question about reasoning on new principles, and of laying down, à priori, rules for the interpretation of nature; the only guides for us to follow are the appearances themselves; for that which we have in view is not a set of systems and vain opinions, but much rather a life exempt from every kind disquietude.

    "The heavenly phænomena do not inspire those who give different explanations of them, conformable with appearances, instead of explaining them by hypothesis, with any alarm. But if, abandoning hypothesis, one at the same time renounces the attempt to explain them by means of analogies founded on appearances, then one is placing one’s self altogether at a distance from the science of nature, in order to fall into fables.

    "It is possible that the heavenly phænomena may present some apparent characteristics which appear to assimilate them to those phænomena which we see taking place around ourselves, without there being any real analogy at the bottom. For the heavenly phænomena may depend for their production on many different causes; nevertheless, we must observe the appearances presented by each, and we must distinguish the different circumstances which attach to them, and which can be explained in different manners by means of analogous phænomena which arise under our eyes.

    "The world is a collection of things embraced by the heaven, containing the stars, the earth, and all visible objects. This collection, separated from the infinite is terminated by an extremity, which is either rare, or dense, or revolving, or in a state of repose, or of a round, or triangular, or some shape or other in fact, for it may be any shape the dissolution of which must bring the destruction of everything which they embrace. In fact, it can take place in every sort of way, since there is not one of those things which are seen which testifies against this world in which we cannot detect any extremity; and that such worlds are infinite in number is easily seen, and in the [mu-epsilon-tau-alpha-xi?-omicron-sigma-mu-iota-omicron-eta: metacosmos?], as we call the space between the worlds, being a huge space made up of plenum and void, but not, as some philosophers pretend, an immensity of space absolutely empty. This production of a world may be explained thus: seeds suitably appropriated to such an end may emanate either from one or from several worlds, or from the space that separates them; they flow towards a particular point where they become collected together and organized; after that, other germs come to unite them together is such a way as to form a durable whole, a basis, a nucleus to which all successive additions unite themselves.

    "One must not content one’s self in this question with saying, as one of the natural philosophers has done, that there is a reunion of the elements, or a violent motion in the void under the influence of necessity, and that the body which is thus produced increases until it come to crash against some other; for this doctrine is contrary to appearances.

    "The sun, the moon, and the other stars, were originally formed separately, and were afterwards comprehended in the entire total of the world. All the other objects which our world comprises, for instance, the earth and the sea, were also formed spontaneously, and subsequently gained size, by the addition and violent movement of light substances, composed of elements of fire and air, or even of these two principles at once. This explanation, moreover, is in accordance with the impressions of the senses.

    "As to the magnitude of the sun and of the other stars, it is, as far as we are concerned, such as it appears to us to be."

    (This same doctrine is reproduced, and occurs again in the eleventh book of his treatise on Nature; where he says, "if the distance has made it lose is size, á fortiori, it would take away its brilliancy; for color has not, any more than size, the property of traversing distance without alteration.")

    "But considered by itself, the sun may be a little greater or a little smaller than it appears; or it may be just such as it looks; for that is exactly the case with the fires of common occurrence among men, which are perceived by the senses at distance. Besides, all the difficulties on this subject will be easily explained if one attends to the clear evidence of the perceptions, as I have shown in my books about Nature.

    "The rising and setting of the sun, of the moon, and of the stars, may depend on the fact of their becoming lighted up, and extinguished alternately, and in order which we behold. One may also give other reasons for the phænomenon, which are not contradicted by any sensible appearances; accordingly, one might explain them by the passage of the stars above and below the earth, for the impressions of the senses agree also with this supposition.   

    "As to their motion, one may make that depend on the circular movement of the entire heaven. One may also suppose that the stars move, while the heaven itself is immovable; for there is nothing to prevent the idea that originally, before the formation of the world, they may have received, by the appointment of fate, an impulse from east to west, and that now their movement continues in consequence of their heat, as the fire naturally proceed onwards in order to seek the nourishment which suits it.

    "The intertropical movements of the sun and moon may depend, either on the obliquity impressed by fate on the heaven at certain determined epochs, or on the resistance of the air, or on the fact that these ignited bodies stand in need of being nourished by a matter suitable to their nature, and that this matter fails them; or finally, they may depend on the fact their having originally received an impulse which compels them to move as they do describing a sort of spiral figure. The sensible evidence does not in the least contradict these different suppositions, and all those of the same kind which one can form, having always a due regard to what is possible, and bring back each phænomenon to its analogous appearances in sensible facts, without disquieting one’s self about the miserable speculations of the astrologers.

    "The evacuations and subsequent replenishing of the moon may depend either on a conversion of this body, or on the different forms which the air when in a fiery state can adopt, or perhaps to the interposition of another body, or lastly, to some one of the causes by which one gives account of the analogous phænomena which pass under our eyes. Provided, however, that one does not obstinately adopt an exclusive mode of explanation; and that, for want of knowing what is possible for a man to explain, and what is inaccessible to his intelligence; one does not throw one’s self into interminable speculations.

    It may also be possibly the case that the moon has a light of her own, or that she reflects that of the sun. For we see around us many objects which are luminous of themselves, and many other which have only a borrowed light. In a word, one will not be arrested by any of the celestial phænomena, provided that one always recollects that there are many explanations possible; that one examines the principles and reasons which agree with this mode of explanation, and that one does not proceed in accounting for the facts which do not agree with this method, to suffer one’s self to be foolishly carried away, and to propose a separate explanation for each phænomenon, sometimes in one way, and sometimes in another.

    "The appearance of a face in the orb of the moon, may depend either on a displacement of its parts, or on the interposition of some obstacle, or on any other cause capable of accounting for such an appearance. For one must not neglect to apply this same method to all the heavenly phænomena; for, from the moment when one comes to any point of contradiction to the evidence of the senses, it will be impossible to posses perfect tranquillity and happiness.

    "The eclipses of the sun and moon may depend either on the fact that these celstial bodies extinguish themselves, a phænomenon which we often see produced under our eyes, or on the fact of other bodies, the earth, the heaven, or something else of the same kind interposing, between them and us. Besides, we must compare the different modes of explanation appropriate to phænomena, and recollect that it is not impossible that many causes may at one and the same time concur in their production."

    (He says the same thing in the twelfth book of his treatise on Nature; and adds that the eclipses of the sun arise from the fact that it penetrates into the shade of the moon, to quit it again presently; and the eclipse of the moon from the fact of its entering into the shade of the earth. We also find the same doctrine asserted by Diogenes, the Epicurean, in the first book of his Select Opinions.)

    "The regular and periodical march of these phænomena has nothing in it that ought to surprise us, if we only attend to the analogous facts which take place under our eyes. Above all things let us beware of making the Deity interpose here, for that being we ought to suppose exempt from all occupation and perfectly happy; otherwise we shall be only giving vain explanations of the heavenly phænomena, as has happened already to a crowd of authors. Not being able to recognize what is really possible, they have fallen into vain theories, in supposing that for all phænomena there was but one single mode of production, and in rejecting all other explanations which are founded on probability; they have adopted the most unreasonable opinions, for want of placing in the front the study of heavenly phænomena, and of sensible facts, which ought to serve to explain the first.

    "The differences in the length of nights and days may arise from the fact that the passage of the sun above the earth is more or less rapid; and more or less slow, according to the length of the regions which it as to pass through. Or, again, to the fact certain regions are passed through more rapidly than others, as is seen to be the case by our own eyes, in those things to which we can compare the heavenly phænomena. As to those who on this point admit only one explanation as possible, they put themselves in opposition to facts, and lose sight of the bounds set to human knowledge.

    "The prognostics which are derived from the stars may, like those which we borrow from animals, arise from a simple coincidence. They may also have other causes, for example, some change in the air; for these two suppositions both harmonize equally with facts; but it is impossible to distinguish in what case one is to attribute them to the one cause or to the other.

    "The clouds may be formed either by the air condensed under the pressure of the winds, or by the agency of atoms set apart for the end, or by emanations from the earth and waters, or by other causes. For there are a great number which are all equally able to produce this effect. When the clouds clash with one another, or undergo any transformation, they produce showers; and the long rains are caused by the motion of the clouds when moved from places suitable to them through the air, when a more violent inundation than usual takes place, from collections of some masses calculated to produce these effects.

    "Thunder possibly arises from the movement of the winds revolving in the cavities of the clouds; of which we may see an image in vessels in our own daily use. It may also arise from the noise of fire acted upon by the wind in them, and from the tearings and ruptures of the clouds when they have received a sort of crystaline consistency. In a word, experience drawn from our sense, teaches us that all these phænomena, and that one in particular, may be produced in many different manners.

    "One may also assign different causes to lightning; either the shock and collision of the clouds produce a fiery appearance, which is followed by lightning; or the lighting up of the clouds by the winds, produces this luminous appearance; or the mutual pressure of the clouds, or that of the wind against them, disengages the lightning. Or, one might say, that the interception of the light diffused from the stars, arrested for a time in the bosom of the clouds, is driven from them subsequently by their own movements, and by those of the winds, and so escapes from their sides; that the lightning is an extremely subtle light that evaporates from the clouds; that the clouds which carry the thunder are collected masses of fire; that the lighting arises form the motion of the fire, or from the conflagration of the wind, in consequence of the rapidity and continuousness of its motion. One may also attribute the luminous appearance of lightning to the rupture of the clouds under the action of the winds, or to the fall of inflammable atoms. Lastly, one may easily find a number of other explanations, if one applies to sensible facts, in order to search out the analogies which they present to the heavenly phænomena.

    "Lightning precedes thunder, either because it is produced at the same moment that the wind falls on the cloud, while the noise is only heard at the instant when the wind has penetrated into the bosom of the cloud; or, perhaps, the two phænomena being simultaneous, the lightning arrives among us more rapidly than the noise of the thunder-bolt, as is in fact remarked in other cases when we see at a instance the clash of two objects.

    "The thunderbolt may be produced either by a violent condensation of the winds, or by their rapid motion and conflagrations. It may arise from the fact of the winds meeting in places which are too dense, in consequence of the accumulation of clouds, and then a portion of the current detaches itself and proceeds towards the lower situations; or else it may be caused by the fire which is contained in the bosom of the clouds precipitating itself downwards. As one may suppose that an immense quantity of fire being accumulated in the clouds dilates, violent bursting the substance which envelops it, because the resistance of the center hinders it from proceeding further. This effect is especially produced in the neighborhood of high mountains; and, accordingly, they are very frequently struck with the thunderbolts. In short, one may give a number of explanations of the thunderbolt; but we ought, above all things, to be on our guard against fables, and this one will easily be, if one follows faithfully the sensible phænomena in the explanation of these things, which are not perceived, except indirectly.

    "Hurricanes may be caused either by the presence of a cloud, which a violent wind sets in motion and precipitates with a spiral movement towards the lower regions, or by a violent gust which bears a cloud into the neighborhood of some other current, or else by the mere agitation of the wind by itself, when air is brought together from the higher regions and compressed without being able to escape on either side, in consequence of the resistance of the air which surrounds it; when the hurricane descends towards the earth, then there result whirlwinds in proportion to the rapidity of the wind that has produced them; and this phænomenon extends over the sea also.

    "Earthquakes may arise from the wind penetrating into the interior of the earth, or from the earth itself receiving incessantly the addition of exterior particles, and being in incessant motion as to its constituent atoms, being in consequence disposed to a general vibration. That which permits the wind to penetrate is the fact that falls take place in the interior, or that the air being impressed by the winds insinuates itself into the subterranean caverns. The movement which numberless falls and the reaction of the earth communicates to the ground, when this motion meets bodies of greater resistance and solidity, is sufficient to explain the earthquakes. One might, however, give an account of them in several other ways.

    "Winds are caused, either by the successive and regular addition of some foreign matter, or else by the reunion of a great quantity of water; and the differences of the winds may arise form the fact that some portions of this same matter fall into the numerous cavities of the earth, and are divided there.

    "Hail is produced by an energetic condensation acting on the ethereal particles which the cold embraces in every direction; or, in consequence of less violent condensation acting however on aqueous particles, and accompanied by division, in such a manner as to produce, at the same time, the reunion of certain elements and of the collective masses; or by the rupture of some dense and compact mass which would explain at the same time, the numerousness of the particles and their individual hardness. As to the spherical form of the hail, one may easily account for that by admitting that the shocks which it receives in every direction make all the angles disappear, or else that at the moment when the different fragments are formed, each of them is equally embraced on all sides by aqueous or ethereal particles.

    "Snow may be produced by a light vapor full of moisture which the clouds allow to escape by passage intended for that end, when they are pressed, in a corresponding manner, by other clouds, and set in motion by the wind. Subsequently, these vapors become condensed in their progress under the action of the cold which surrounds the clouds in the lower regions. It may also be the case that this phænomena is produced by clouds of slight density as they become condensed. In this case the snow which escapes from the clouds would be the result of the contact, or approximation of the aqueous particles, which in a still more condensed state produce hail. This effect is most especially produced in the air. Snow again, may result from the collection of clouds previously condensed and solidified; or from a whole army of other causes.

    "Dew proceeds from a reunion of particles contained in the air calculated to produce this moist substance. These particles may be also brought from places which are moist or covered with water (for in those places, above all others, it is that dew is abundant). These then reunite, again resume their aqueous form, and fall down. The same phænomena takes place in other cases before our own eyes under many analogies.

    "Hoarfrost is dew congealed by the influence of the cold air that surrounds it.

    "Ice is formed either by the detrition of round atoms contained in the water, and the reunion at scalene and acute angles of the atoms which exist in the water, or by an addition from without of these latter particles, which penetrating into the water, solidify it by driving away an equal amount of round atoms.

    "The rainbow may be produced by the reflection of the solar rays on the moist air; or it may arise from a particular property of light and air, in virtue of which these particular appearances of color are formed, either because the shade which we perceive result directly from this property, or because, on the contrary, it only produces a single shade, which, reflecting itself on the nearest portion of the air, communicates to them the tints which we observe. As to the circular form of the rainbow, that depends either on the fact of the sight perceiving an equal distance in every direction, or the fact of the atoms taking this form when reuniting in the air; or it may be caused by its detaching from the air which moves towards the moon, certain atoms which, being reunited in the clouds, give rise to this circular appearance.

    "The lunar halo arises from the fact of the air, which moves towards the moon from all quarters, uniformly intercepting the rays emitted by this heavenly object, in such a way as to form around it a sort of circular cloud which partially veils it. It may also arise from the fact of the moon uniformly rejecting from all quarters, the air which surrounds it, in such a manner as to produce this circular and opaque covering. And perhaps this opaqueness may be caused by some particle which some current brings form without; perhaps also, the heat of communicates to the moon the property of emitting by the pores in tits surface, the particles by which this effect is produced.

    "Comets arise either from the fact, that in the circumstances already stated, there are partial conflagrations in certain points of the heaven; or, that at certain periods, the heaven has above our heads a particular movement which causes them to appear. It may also be the case, that being themselves endowed with a peculiar movement, they advance at the end of certain periods of time, and in consequence of particular circumstances, towards the places which we inhabit. The opposite reasons explain their disappearance.

    "Certain stars return to the same point in accomplishing their revolutions; and this arises, not only as has been sometimes believed, from the fact of the pole of the world, around which they move, being immovable, but also from the fact that the gyrations of the air which surrounds them, hinder them from deviations like the wandering stars. Perhaps also, this may be caused by the fact, that except in the route in which they move, and in which we perceive them, they do not find any material suitable to their nature. One may also explain this phænomenon in many other manners, reasoning according to sensible facts; thus, it is possible that certain stars may be wandering because that is the nature of their movements, and, for the same reason, others may be immovable. It is also possible, that the same necessity which has originally given them their circular movement, may have compelled some to follow their orbit regularly, and have subjected others to an irregular process; we may also suppose that the uniform character of the center which certain stars traverse favor their regular march, and their return to a certain point; and that in the case of other, on the contrary, the differences of the center produce the changes which we observe. Besides, to assign one single cause to all these phænomena, when the experience of our senses suggests us several, is folly. It is the conduct of ignorant astrologers covetous of a vain knowledge, who assigning imaginary causes to facts, wish to leave wholly to the Deity the care of the government of the universe.

    "Some stars [the planets] appear to be left behind by others in their progress; this arises either from the fact of their having a slower motion, though traversing the same circle; or, because, that they are drawn on by the same propelling power, they have, nevertheless, a movement proper to themselves in a contrary direction; or it may be caused by the fact that, though all are placed in the same sphere of movement, still some have more space to traverse, and others less. To give one uniform and positive explanation of all these facts, is not consistent with the conduct of any people but those who love to flash prodigies in the eyes of the multitude.

    "Falling stars may be particles detached from the stars, or fragments resulting from their collision; they may also be produced by the fall of substances which are set on fire by the action of the wind; by the reunion of inflammable atoms which are made to come together so as to produce this effect by a sort of reciprocal attraction; or else by the movement which is produced in consequence of the reunion of atoms in the very place where they meet. It may also happen that the light vapors reunite and become condensed under the form of clouds, that they then take fire in consequence of their rotary motion, and that, bursting the obstacles which surround them, they proceed towards the places whither the force by which they are animated drags them. In short, this phænomenon also may admit a great number of explanations.

    "The forecasts which are drawn from certain animals arise from a fortuitous concourse of circumstances; for there is no necessary connection between certain animals and winter. They do not produce it; nor is there any divine nature sitting aloft watching the exits of these animals, and then fulfilling signs of this kind. Nor can such folly as this occur to any being who is even moderately comfortable, much less to one which is possessed of perfect happiness.

    "Imprint all these precepts in your memory, O Pythocles, and so you will easily escape fables, and it will be easy for you to discover other truths analogous to these. Above all, apply yourself to the study of general principles, of the infinite, and of questions of this kind, and to the investigation of the different criteria and of the passions, and to the study of the chief good, with a view to which we prosecute all our researches. When these questions are once resolved, all particular difficulties will be made plain to you. As to those who will not apply themselves to these principles, they will neither be able to give a good explanation of these same questions, nor to reach that end to which all our researches tend."