The Lives and Opinions of Eminent Philosophers

by Diogenes Laertius

“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 of 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 bringing back each phænomenon to its analogous appearances in sensible facts, without disquieting one’s self about the miserable speculations of the astronomers.

“The evacuations and subsequent replenishings 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 others 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 possess perfect tranquillity and happiness.

“The eclipses of the sun and moon may depend either on the fact that these stars 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 eclipses 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 the 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 has to pass through. Or, again, to the fact that 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 that 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.