360 Royal Society : Prof. Faraday's Experimental 



contiguous particles, the author employed, as an electrometer, the 

 torsion balance of Coulomb with certain alterations and additions ; 

 and for deciding that of specific inductive capacity, a new apparatus, 

 constructed for that express purpose. This apparatus consisted of 

 two hollow brass spheres, of very unequal diameters, the smaller 

 placed within the larger, and concentric with it ; the interval be- 

 tween the two being the space through which the induction was to 

 be effected. The apparatus had a tube in the lower part, furnished 

 with a stop-cock, by means of which it might be connected with an 

 air-pump or filled with any required gas. In place of the lower hemi- 

 spherical shell of air, occupying the interval between the two 

 spheres, any solid dielectric, of the same form, such as shell-lac, 

 glass, or sulphur, might be substituted. Two of these instruments, 

 precisely similar in every respect, were constructed, and the author 

 ascertained that the inductive power was the same in both, by alter- 

 nately charging each and dividing the charge with the other, and 

 finding that, in all cases, the charge remaining in the one, and also 

 that received by the other, was very nearly half the original charge. 



The experiments on which the author principally relies in support 

 of the correctness of his views relative to induction being exerted in 

 curved lines, are the following : a brass ball being laid on the top 

 of an excited cylinder of shell-lac placed vertically, the charge 

 which a carrier ball received when brought to different points near 

 to the brass sphere was measured by means of the electrometer ; and it 

 was inferred, from the character of the electricity, that the charge 

 was one by induction, and from its measure, that it proceeded in 

 curved lines. By substituting for the brass sphere a disc of metal 

 above the shell-lac cylinder, it was found that when the carrier ball was 

 brought near to the middle of the disc no charge was communicated, 

 although a sensible one was obtained at the edge of the disc, and 

 also at a point above its centre, further removed from the excited 

 cylinder. Corresponding and very striking results were obtained 

 when a brass hemisphere was placed on the top of the cylinder of lac. 

 The charge communicated at the centre of the hemisphere was only 

 one-third of that obtained at the edge of its periphery ; but by taking 

 it at a point at some height above the centre, and consequently much 

 further removed from the inducing cause, the charge was nearly 

 equal to that of the periphery. Here, the author remarks, the in- 

 duction fairly turned a corner, exhibiting both the curved lines or 

 courses of its action, when disturbed from their rectilineal form by 

 the shape, position and condition of the metallic hemisphere ; and 

 also a lateral tension, so to speak, of these lines on one another ; all 

 depending on induction being an action of the contiguous particles 

 of the dielectric thrown into a state of polarity and tension, and mu- 

 tually related by their forces in all directions. In the foregoing ex- 

 periments the dielectric was air; but they were afterwards varied by 

 substituting a fluid, as oil of turpentine, and likewise a few solid 

 dielectrics, namely, shell-lac, sulphur, carbonate and borate of lead, 

 flint-glass, and spermaceti, and with these, corresponding results 



