The Lives and Opinions of Eminent Philosophers

by Diogenes Laertius

“Hoar-frost 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 re-union 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 colour are formed, either because the shades which we perceive result directly from this property, or because, on the contrary, it only produces one single shade, which, reflecting itself on the nearest portions 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 re-uniting in the air; or it may be caused by its detaching from the air which moves towards the moon, certain atoms which, being re-united 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 star, 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 particles which some current brings from without; perhaps also, the heat communicates to the moon the property of emitting by the pores in its 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 immoveable, 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 immoveable. 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 progress; we may also suppose that the uniform character of the centre which certain stars traverse favour their regular march, and their return to a certain; and that in the case of others, on the contrary, the differences of the centre 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 astronomers 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 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, though 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 re-union 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 re-union of atoms in the very place where they meet. It may also happen that the light vapours re-unite and become condensed under the form of clouds, that they then take fire in consequence of their rotatory 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 of a great number of explanations.

“The presages 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 accomplishing 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.”