214 KINETIC THEORIES OF GRAVITATION. 



in a competitive memoir on the cause of " The Mutual Inclination of 

 the Planetary Orbits," which obtained the prize of the French Academy 

 of Sciences in 1734. This treatise is divided into four parts, the first 

 three of which are occupied with his exposition of the cause of gravita- 

 tion, and the fourth with the main question proposed.* 



Referring to the respective systems of Descartes and Newton, Bernou- 

 illi finds in each "■' iusurtnountable difficulties," hence " a just mean be- 

 tween the two appears the safer course. . . . The gravitation of 

 the planets toward the center of the sun, and the weight of bodies 

 toward the center of the earth, are not caused either by the attraction 

 of Newton, or by the rotary force of the vortex medium of Descartes, 

 but by the immediate impulsion of a substance which under the form 

 of what 1 call a ' central torrent,' is continually thrown from the whole 

 circumference of the vortex to its center, and consequently impresses on 

 all bodies encountered by it in its path the same tendency toward the 

 center of the vortex. . . . And all that Newton has derived from 

 his ' attractions' are by my theory, derived from the impulsions of the 

 central torrent.^'' t 



"According to my system, two kinds of matter are conceived as occupy- 

 ing planetary space, and also two principal moveu)ents in the celestial vor- 

 tex. One of these materials I conceive as perfectly fluid, or 1 would say, 

 actually divisible without limit; that is, it is not composed of elementary 

 cori^uscles, as ordinary fluids are conceived, which according, the num- 

 ber and size of their constituent particles, present more or less sensible 

 resistance to bodies moving in them, but being perfectly uniform and 

 without structure, is also without resistance." This matter is called the 

 primal element ; which was employed by the Creator in forming the cor- 

 puscles of sensible matter, definite small portions being compacted 

 together into the coherent molecules of matter of the second element. 



" Matter of the primal element, being perfectly fluid without coher- 

 ence, presents no resistance to bodies moving within it ; for the resistance 

 of fluids comes only from the inertia of the molecules of which they are 

 composed."! This primal element, being without constituent parts and 

 without inertia, is as the author states, the same in eft'ect as a perfect 

 vacuum. 



" The celestial vortex is composed in great part of the primal element, 

 in which is mingled however, a considerable portion of the second ele- 

 ment." According to Beruouilli's view, " the rotation of this vortex is not 

 so rapid as to carry the planets around the sun, as Descartes assumed." 

 In fact, its rotary velocity is in a subsequent portion of the memoir 

 stated to be so low as to amount to only about one two hundred and 

 thirtieth of the orbital velocity of the planets, an approximation to the 



' Publislied in the Pieces de Prix de V Academic de Paris, torn, v, and included in bis 

 collected works under the title Essai dUine Nouvelle Physique Celeste. 



tJohannia Beruoullii, Opera Omnia, A vols. 4to. Lausanne and Geneva, 174'2; vol. iii, 

 Sec. viii, pp. 270,271. 



t Loco citat., sections x and xvi, pp. 273, 27G. 



