426 Mr. Faraday's Researches i7i Electricity. {Series XL) 



titles so small as not to be distinguished in the apparatus I 

 have used. It must be remembered, however, that in the 

 gaseous experiments the gases occupy all the space o, o, (fig. 

 1.) between the inner and the outer ball, except the small 

 portion filled by the stem; and the results, therefore, are 

 twice as delicate as those with solid dielectrics. 



1294. The insulation was good in all the experiments re- 

 corded, except Nos. 10, 15, 21, and 25, being those in which 

 ammonia was compared with other gases. When shell-lac is 

 put into ammoniacal gas its surface gradually acquires con- 

 ducting power, and in this way the lac part of the stem within 

 was so altered, that the ammonia apparatus could not retain a 

 charge with sufficient steadiness to allow of division. In these 

 experiments, therefore, the other apparatus was charged ; its 

 charge measured and divided with the ammonia apparatus 

 by a quick contact, and what remained untaken away by the 

 division again measured (1281.). It was so nearly one half 

 of the original charge, as to authorize, with this reservation, 

 the insertion of ammoniacal gas amongst the other gases, as 

 having equal power with them. 



1295. Thus inductioji appears to be essentially an action 

 of contiguous particles, through the intermediation of which 

 the electric force, originating or appearing at a certain place, 

 is propagated to or sustained at a distance, appearing there 

 as a force of the same kind exactly equal in amount, but op- 

 posite in its direction and tendencies (IIG^.). Induction re- 

 quires no sensible thickness in the conductoi's which may be 

 used to limit its extent ; an uninsulated leaf of gold may be 

 made very highly positive on one surface, and as highly ne- 

 gative on the other, without the least interference of the two 

 states whilst the inductions continue. Nor is it affected by 

 the nature of the limiting conductors, provided time be al- 

 lowed, in the case of those which conduct slowly, for them to 

 assume their final state (1170.). 



1296. But with regard to the dielectrics or insulating media, 

 matters are very different (1167.). Their thickness has an 

 immediate and important influence on the degree of induc- 

 tion. As to their quality, though all gases and vapours are 

 alike, whatever their state, amongst solid bodies, and between 

 them and gases, there are differences which prove the exist- 

 ence of specific inductive capacities^ these differences being in 

 some cases very great. 



1297. The direct inductive force, which may be conceived 

 to be exerted in lines between the two limiting and charged 

 conducting surfaces, is accompanied by a lateral or transverse 



