KINETIC THEORIES OF GRAVITATION. 271 



a ponderable atom is not in the simple ratio of its mass; for if this mass 

 equalled that of an tether atom, the attraction would be nil. If there 

 exist ponderable atoms of different masses their rate of fail would be 

 uneqal. If there were but one kind of ponderable atom, all bodies would 

 fall with equal velocity. Experience seems to justify the last hypothesis; 

 but very slight differences of mass in the ponderable atoms would suffice 

 to determine the formation of chemical elements of very different 

 atomic weights, and an inequality of their fall would escape unadvised 

 observers.' 1 



After affirming the law of distance, M. Boisbaudrau says : " In conse- 

 quence of the inertia of the rether, attraction is not proportional to the 

 real masses, but no more is it to the number of ponderable atoms con- 

 tained in a body. The vis viva of the atoms of sether, however great, 

 has a finite value." Lastly, he remarks: "It is to the longitudinal 

 vibrations of the aether that I attribute the cause of weight. 1 '* 



^Neither the hypothesis of M. Leray, nor that of M. Boisbaudrau, pre- 

 sents any feature of special novelty, requiring comment. 



GUTHRIE. 1870. 



In 1870, Prof. Frederick Guthrie published an account of some inter- 

 esting experiments "On Approach caused by Vibration," unaware at 

 the time of the earlier labors of Dr. Guyot in the same direction. He 

 found that a card suspended near a vibrating tuning-fork was urged 

 toward the fork, and by varying the experiment with smoke, with cork, 

 with calcined magnesia, with floss cotton, with a second suspended 

 tuning-fork, with brass disks, etc., he obtained similar results. At the 

 termination of his experiments he thus sums up : " The experimental 

 results appear to me to point to the following conclusions : whenever 

 an elastic medium is between two vibrating bodies, or between a vibrat- 

 ing body and one at rest, and when the vibrations are dispersed in con- 

 sequence of their impact on one or both of the bodies, the bodies will 

 be urged together. The dispersion of a vibratiou produces a similar 

 effect to that produced by the dispersion of the air-current in Clement's 

 experiment; and, like the latter, the effect is due to the pressure ex- 

 erted by the medium-, which is in a state of higher tension [or pressure] 

 on the side of the body furthest from the origin of vibration than on 

 the side toward it. In mechanics — in nature — there* is no such thing 

 as a pulling force. Though the term attraction may have been occa- 

 sionally used in the above to denote the tendency of bodies to approach, 

 the line of conclusions here indicated tends to argue that there is no 

 such thing as attraction in the sense of a pulling force, and that two 

 utterly isolated bodies cannot influence one another. If the aetherial 

 vibrations which are supposed to constitute radiant heat resemble the 

 a3rial vibrations which constitute sound, the heat which all bodies pos- 



* Comptes Eendus, 20th September, 1869, vol. lxix, pp. 703, 704. 



