Kinetic Theories of Gravitation. William Bower Taylor
which strike the solid bodies perpetually should be insensible."[4]
Not only does the "gravific fluid" utterly fail to give an approximate representation of the actual conditions of the planetary movements, but as must be evident, it will not permit the continued existence of any such movements. A mass moving in free space in any direction excepting directly toward a similar mass, must receive a more active shower of corpuscles in its front than in its rear, and must thus be retarded by a differential of energy directly proportioned to its velocity. Every planet must accordingly encounter a tangential resistance to its orbital motion, proportional to its own gravitation and to its velocity.
As illustrative of the different estimates of this hypothesis formed by distinguished men, the following citations may be permitted. M. Pierre Prevost, professor or philosophy and general physics in the University of Geneva, published two years after the death of Lesage, an account of his writings, in which, after a sketch of his corpuscular hypothesis, he remarks, "I pause at the foot of this majestic edifice with a sentiment of hope ; persuaded that the labors of the founder will not be suffered to perish, and that men of genius will share with me the admiration it has inspired."[5] And Professor Tait regards it as "the only plausible answer to this [great problem] which has yet been propounded."[6] Sir John Herschel, on the other hand, has remarked, " The hypothesis of Lesage which assumes that every point of space is penetrated at every instant of time by material particles sui generis, moving in right lines in every possible direction, and impinging upon the [221] material atoms of bodies, as a mode of accounting for gravitation, is too grotesque to need serious consideration ; and besides will render no account of the phenomenon of elasticity."[7]
As an interesting illustration of Lesage's range of intellectual activity, it may be mentioned that to him belongs the credit of having devised, constructed, and operated, in his native city, Geneva, in 1774, the first working electric telegraph. t His system consisted in the employment of an insulated wire for each letter, terminating in an electroscope at the receiving-station. He also wrote a Dissertation sur l'electricite applique a la Transmission des Nouvelles :—the first treatise on the electric telegraph.[8]
1 ↑ Popular Astronomy, book xxiii, chap. 27, vol. ii, p. 468.
2 ↑ Lectures on Recent Advances in Physical Science, London, 1875, Lect. xii. p. 300.
3 ↑ Encyclopaedia Britannica, ninth edition, 1875, article "Atom," vol. iii, pp. 43, 47.
4 ↑ North British Review, March, 1868, vol. xlviii, p. 126 of American edition.
5 ↑ Notice de la Vie et des Ècrits de G.-L. Le Sage, published at Geneva in 1805.
6 ↑ Lectures on Physical Science, loco citat, p. 291
7 ↑ Fortnightly Review, July 1, 1865, vol. i, p. 438.
8 ↑ the earliest attempt to apply frictional lectricity to telegraphy seems to have been made by Lesage, of Geneva, who, in 1774, constructed a telegraph consisting of twenty-four insulated wires." (George B. Prescott, Electricity and the Electric Telegraph, 8vo, N. Y., 1877, chap, xxix, p. 414.)
Euler, 1760
Leonard Euler, the eminent Swiss mathematician and philosopher, (a pupil of Beruouilli previously referred to,) entertained an indefinite impression that the setherial medium is in some way a connecting link between the celestial bodies, inducing that mutual tendency to approach commonly called "attraction." Only some dozen years later than the date of Lesage's first conception, he briefly discussed the subject in his celebrated "Letters" commencing in 1760.
He thus comments on the action of gravity : " Supposing a hole made in the earth through its center; it is clear that a body at the very center must entirely lose its gravity, as it could no longer move in any direction whatever, all those of gravity tending continually toward the center of the earth. Since then a body has no longer gravity at the center of the earth, it will follow that in descending to this center, its gravity will be gradually diminished; and we accordingly conclude that a body penetrating into the bowels of the earth loses its gravity in proportion as it approaches the center. It is evident then that neither the intensity nor the direction of gravity is a consequence from the nature of any body, as not only its intensity is variable, but likewise its direction, which, on passing to the antipodes, becomes quite contrary."[1]
After some further exposition of the efi'ects of gravitation, as observed in the courses of the planets, Euler indulges in some speculation on the probable nature of this influence. " But in attempting to dive into the mysteries of nature, it is of importance to know if the heavenly bodies act upon each other by impulsion or by attraction ; if a certain subtile invisible matter impels them toward each other ; or if they are [222] endowed with a secret or occult quality, by which they are mutually attracted. On this question philosophers are divided. Some are of opinion that this phenomenon is analogous to an impulsion j others maintain with Newton, and the English in general, that it consists in attraction."[2]
"To avoid all confusion which might result from this mode of expression, it ought rather to be said that bodies move as if they mutually attracted each other. This would not decide whether the powers which act on bodies reside in the bodies themselves or out of them ; and this manner of speaking might thus suit both parties. Let us confine ourselves to the bodies which we meet with on the surface of the earth. Every one readily admits that all these would fall downward, unless they were supported. Now the question turns on the real cause of this fall. Some say that it is the earth which attracts these bodies, by an inherent power natural to it ; others that it is the tether, or some other subtile or invisible matter, which impels the body downward, so that the effect is nevertheless the same in both cases.
" This last opinion is most satisfactory to those who are fond of clear principles in philosophy, as they do not see how two bodies at a distance can act upon each other if there be nothing between them. … Let us suppose that before the creation of the world, God had created only two bodies, at a distance from each other ; that absolutely nothing existed outside of them, and that they were in a state of rest; would it be possible for the one to approach the other, or for them to have a propensity to approach? How could the one feel the other at a distance ? Whence could arise the desire of approaching? These are perplexing questions. But if you suppose that the intermediate space is filled with a subtile matter, we can comprehend at once that this matter may act upon the bodies by impelling them. The effect would be the same as if they possessed a power of mutual attraction. Now as we know that the whole space which separates the heavenly bodies is filled with a subtile matter called aether, it seems more reasonable to ascribe the mutual attraction of bodies to an action which the aether exercises upon them, though its manner of acting may be unknown to us, than to have recourse to an unintelligible property As the idea of all occult qualities is now banished from philosophy, attraction ought not to be considered in this sense."[3]
It does not appear how so vague and inexplicable a supposition is calculated to commend itself "to those who are fond of clear principles in philosophy." In his anxiety to avoid an "occult quality " in matter, this learned writer seems quite unconscious of the fact that by investing his aether with an "unknown manner of acting," he is just as fatally "having recourse to an unintelligible property." Certainly, just as [223] "perplexing questions " are suggested by the hypothesis of aether pressure, as by the hypothesis of" an original "propensity to approach."