LAWS OF ELECTRICAL ACTION AT A DISTANCE. 237 



64. Upon considering attentively the march of the attractive force in the body h 

 excited by induction, it would appear that the intensity of the induced accumulation 

 is not subject to the same law as observed in permanently electrified bodies (16.), the 

 force in the one case being as the induced accumulation simply, in the other as the 

 square of the quantity communicated. 



The cause of this difference may possibly be traced to an essential difference in 

 the nature of the respective accumulations. In the induced accumulation, the at- 

 tractive force arises from the change effected in the electricity originally possessed by 

 the body itself: hence the accumulation by induction may be considered rather as a 

 species of electrical development in the neutral body. Now the quantity of developed 

 electricity being altogether a free quantity, it must consequently be always as the 

 exciting cause directly, all other things being the same ; the induced action on the 

 neutral body will therefore be always as the free action of the electricity accumulated 

 on the charged conductor, as is shown by experiment {s.), 



65. This influence of free electricity on a neutral conductor which we have been 

 just considering, is quite independent of atmospheric pressure, it being precisely the 

 same in a partially exhausted receiver as in air. I examined the effects of electrical 

 influence in a rarefied medium, by means of two conductors, h h\ attached to rods, 

 passing through the sides of a spherical receiver, as represented in fig. 22. These con- 

 ductors were separable to a greater or less extent by micrometer-screws, s s\ acting on 

 the rods, by which the conductors were sustained, the rods being moveable through 

 airtight collars. 



(u.) By connecting one of the rods with the electroscope A, fig. 1, or with the in- 

 sulated ball b acting on the balance, fig. 9, or with the electrometer, fig. 2, and the 

 opposite rod with a charged conductor or jar, as in the previous cases (17- 18.), the 

 induction between the opposed bodies h K under different atmospheric pressures was 

 easily observed. 



The results of numerous experiments led to the conclusion, that the operation of 

 electricity on distant bodies by induction, is quite independent of atmospheric pres- 

 sure, and is precisely the same in vacuo as in air ; a result which was demonstrable 

 when three fourths of the air was withdrawn from the receiver, the charge employed 

 being such as could be retained on the conductor h under the influence of K placed 

 at three inches' distance. 



66. These experiments were varied by giving the neutral body K a temporary con- 

 nexion with the ground, whilst exposed to the inducing action of A : in this case, as 

 in that above described (21.), the induced effect upon the neutral body is not 

 sensible so long as the accumulation remains on the charged conductor ; but on re- 

 ducing this last to a neutral state, the divergence of the index of the electroscope, or 

 otherwise the attractive effect as indicated by the electrometer (A), or the balance 

 (N), fig. 9, is immediately apparent. 



The general result by this method was the same precisely as in the preceding ex- 



MDCCCXXXIV. 2 I 



