KINETIC THEOEIES OF GRAVITATION. 221 



ferial atoms of bodies, as a mode of accounting for gravitation, is too 

 grotesque to need serious consideration ; and besides will render no ac- 

 count of the phenomenon of elasticity."* 



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 Velectricite applique 

 a la Transmission des Nouvelles : — the first treatise on the electric tele- 

 graph. 



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 direc- 

 tion whatever, all those of gravity tending continually toward the cen- 

 ter 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."! 



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 



''Fortnightly Review, July 1, 1865, vol. i, p. 438. 



f'Tbe earliest attempt to apply frictioual electricity to telegraphy seems to have 

 been raatle by Lesage, of Geneva, who, in 1774, constructed a telegraph consisting of 

 twenty-four insulated w'ires." (George B. Prescott, Electricity and the Electric Tele- 

 graph, 8vo, N. Y., 1877, chap, xxix, p. 414.) 



t Letters a une Princesse d^AUemagne,IjQi. 50, 30th August, 1760. This work, since 

 so popular, was republished in England, " Letters on different subjects in Physics and 

 Philosophy, addressed to a German Princess." Translated from the French by Henry 

 Hunter, 2 vols. 8vo, London, 1802. 



