Induction Apparatus — Effects of Conduction in it. 363 



tricity at the balls h and B (fig. 1.) above and within. It was 

 then discharged, opened, the shell-lac taken out, and its state 

 examined; this was done by bringing the carrier ball near 

 the shell-lac, uninsulating it, insulating it, and then observing 

 what charge it had acquired. As it would be a charge by 

 induction, the state of the ball would indicate the opposite 

 state of electricity in that surface of the shell- lac which had 

 produced it. At first the lac appeared quite free from any 

 charge; but gradually its two surfaces assumed opposite states 

 of electricity, the concave surface, which had been next the 

 inner and positive ball, assuming a positive state, and the 

 convex surface, which been in contact with the negative coat- 

 ing, acquiring a negative state; these states gradually increa- 

 sing in intensity for some time. 



1238. As the return action was evidently greatest instantly 

 after the discharge, I again put the apparatus together, and 

 charged it for fifteen minutes as before, the inner ball posi- 

 tively. I then discharged it, instantly removing the upper 

 hemisphere with the interior ball, and, leaving the shell- 

 lac cup in the lower uninsulated hemisphere, examined its 

 inner surface by the carrier ball as before (1237-)* In this 

 way I found the surface of the shell-lac actually negative, or 

 in the reverse state to the ball which had been in it ; this state 

 quickly disappeared, and was succeeded by a positive condi- 

 tion, gradually increasing in intensity for some time, in the 

 same manner as before. This first negative condition of the 

 surface opposite the positive charging ball is a natural con- 

 sequence of the state of things, the charging ball being in 

 contact with the shell-lac only in a few points. It does not 

 interfere with the general result and peculiar state now under 

 consideration, except that it assists in illustrating in a very 

 marked manner the ultimate assumption by the surfaces of 

 the shell-lac of an electrified condition, similar to that of the 

 metallic surfaces opposed to or against them. 



1239. Glass was then examined with respect to its power 

 of assuming this peculiar state. I had a thick flint glass 

 hemispherical cup formed, which would fit easily into the 

 space o of the lower hemisphere (1188. 1189.); it had been 

 heated and varnished with a solution of shell-lac in alcohol, 

 for the purpose of destroying the conducting power of the 

 vitreous surface. Being then well warmed and experimented 

 with, I found it could also assume the same state^ but not ap- 

 parently to the same degree, the return action amounting in 

 different cases to quantities from 6° to 18°. 



1240. Spermaceti experimented with in the same manner 

 gave striking results. When the original charge had been 



