XXI. ETHER.
WHAT we have said about corporeal substance divisible into particles that are most minute, substantially indivisible, and therefore real atoms, reminds us of what is said and what was said about ether. The most common opinion among the scientists of our time is, firstly, that in the interplanetary spaces there is a corporeal substance extremely rarified; secondly, that this rarefaction consists in the mutual distance of the atoms from each other, which distance, compared with the length of the diameters of these atoms, is so great that (proportions considered) it is as the distance of the stars and the planets from each other lastly, that the nature of these ethereal atoms is the same in all, and is not different from that of the corporeal atoms in this world; so that the ethereal atoms may be said to be the terrestrial atoms themselves extremely diminished and very far from each other. They say too that this ethereal substance is the subject whence light, electricity and heat are diffused. One of the defects observable in modern scientists is their ignorance of many doctrines, often true and important, which the old scientists knew. Hence it is not surprising to hear them say that the conception of ether is modern. In the Cosmos, a French periodical,{1} Courbet says: " La conception d'une substance transmettant la lumière et remplissant l'espace a été introduite pour la première fois dans la science moderne par Hugghens." This pour la première fois is historically a blunder. We had better point out the discrepancy between the ancient and modern scientists about the ether.
10. The modern scientists acknowledge the existence of ether in the interplanetary spaces for the purpose of giving a subject to light and heat; but for the very same reason the old scientists acknowledged the necessity of an ethereal substance. "Aristotle," says St. Thomas, "rejected that error (which denied the existence of ether, and admitted a void), but said that Democritus was wrong in affirming that, if the space between the eye and the object were quite void, we should be able to see the smallest object at an immeasurable distance, -- for instance, an ant in the sky. This is totally impossible.
"We cannot see, unless the organ of sight receives an impression from a visible object but it has been shown that this impression is not received immediately from the visible external objects; and therefore that there must be a medium substance between the sight and the visible thing. If there were a void, there would be no medium capable of being immuted and immuting: so that, if there were an absolute void, we should not see. Democritus fell into the mistake, because he believed that distance impedes our sight of an object just so much as that which is between impedes the operation of the visible thing: but this is false. The reason why distance impedes the sight is this: All bodies are seen under a certain angle of some triangle, or rather of a pyramid, whose base is in the seen object, and the angle is in the eye of the seer. (Omne corpus videtur sub quodam angulo cujusdam trianguli, vel magis pyramidis, cujus basis est in re visa, et angulus est in oculo videntis.) Therefore the greater the object is, compared with the size of the pupil, the more diminished proportionately must the immutation of that visible object be when it comes to the sight. It is evident then that the longer the sides of the triangle or of the pyramid are, the size of the base remaining fixed, the less will the angle be. Therefore the further the object is, the less do we see and the distance may be so great that we cannot see it at all."{2}
From this it is evident that the old scientists admitted interplanetary ethereal substance; that they did not admit the system of emission of light; that they judged light to be not a substance; that they believed it to be a quality derived from a luminous body in the ether, a quality that makes an impression on the pupil, which is enabled thereby to see the object from which that quality is derived by means of the ether, and that the ethereal medium is necessary for seeing, whether the object be far or near. The Angelic Doctor said that omnis lux est effectiva caloris, etiam lux lunae,{3} some centuries before Melloni said so. Evidently therefore it was admitted then that the ethereal substance transmitted heat and was the subject of the medium of heat.
2. The modern scientists commonly admit, as we pointed out before, that the ethereal substance is an aggregation of atoms very distant from each other, if the distance be compared with their diameter: but they maintain the system of undulations, according to which these atoms oscillate in lines parallel to each other and vertical to the luminous ray. There is a difficulty in this that seems to us insuperable: for if the atoms oscillated, they could never come in contact with each other and determine in the others the motion supposed to be given by the luminous object. Hence we should not be able to explain the illumination without the absurdity of admitting collision at a true distance. The Scholastics, as we said, acknowledged a true and proper dilation of the corporeal substances, and not merely the improper: so they never fell into the absurdity of admitting action of ethereal atoms at a true distance. They were indeed very far from having certain experiences that modern scientists have: but the latter are very far from having a perfect knowledge of the nature of things, from which facts ought to be derived.
3. Many modern scientists hold that the ethereal substance is the very substance of the earth and of the air extremely rarefied by the distance between the atoms and therefore action at a distance is not the only difficulty to be objected against them. There are others, for such an ethereal substance ought to have the principal properties of the other corporeal substances -- that of resisting other bodies -- retarding motion, coming into combination with them, &c. Hence the modern author whom we quoted from The Cosmos, is much embarrassed, and believing himself to have shown that the ethereal substance cannot be at all suspected of the least resistance to the planetary bodies, concludes thus : "Nous sommes en présence de deux affirmations absolument opposées. Il n'y a pas de milieu matériel dans l'espace (Him, Faye). Il est sûr que l'espace est rempli d'un milieu capable d'être en vibration, l'éther (Hertz)." Hence Courbet, strangely and without sufficient reason, would introduce into science an opinion taken from Theology, where it teaches that the glorified bodies have the gift of being subtle or penetrable, not resisting earthly bodies nor resisted by them. He says that, if it be necessary, science may without discredit get light from faith, to solve insuperable difficulties in questions of nature.
In the olden time they did not ask whether the ethereal substance resisted the stars and retarded their course, because the conceptions about that were not those of the vulgar. They did not believe it to have the nature of earthly bodies, solid or aerial: did not believe in the possibility of its combining with such and changing its nature. Therefore it was said to be unalterable. The ethereal substance was the firmament. It was not the stars, but that in which the stars are placed, according to the first chapter of Genesis: Fecitque Deus duo luminaria magna. . . . et stellas, et posuit eas in firmamento caeli.
St. Thomas, in answer to the question, Utrum firmamentum sit de natura inferiorum corporum, replies that before Aristotle all the philosophers believed the firmament or heaven to be a substance like in nature to the elementary bodies of this world. Aristotle, he says, proved that the firmament or heaven has not a nature common to other bodies, but has a proper essence: and the later philosophers, persuaded by his reasoning, admitted his doctrine. According to this doctrine the substance of the firmament, in which the stars are, is not heavy, does not alter nor corrupt: and since it has not even a common matter with the other bodies, we cannot, he says (De natura generis), form a conception of it univocally with other bodies, but only an analagous conception. In these days, as in those, we are a long way from having a sure knowledge of the essence of the ethereal substance or firmament; and though we can affirm in accordance with the doctrine above mentioned, that it is the medium and the subject whence light and heat come (as is hinted in the Book of Genesis), we still hesitate, incapable of solving the grave difficulties put forward by Courbet in The Cosmos.
{1} An. 1890, xvi. p. 154, &c.
{2} De amima, LI. Lect. 15.
{3} In II. Sent., Dist. xv. Q. 1. a. 2 ad 5.