22 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XI.) 



coating, acquiring a negative state ; these states gradually increasing 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 positively. I then discharged it, instantly removing the upper hemisphere 

 with the intei'ior ball, and, leaving the shell-lac cup in the lower uninsulated hemi- 

 sphere, 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 condition, 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 consequence of the state of things, the charging ball being in con- 

 tact 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. 1 189.) ; 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 apparently 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 sustained for fifteen or twenty minutes at about 

 500°, the return charge was equal to 95° or 100°, and was about fourteen minutes 

 arriving at the maximum efflect. A charge continued for not more than two or three 

 seconds was here succeeded by a return charge of 50° or 60°. The observations for- 

 merly made (1234.) held good with this substance. Spermaceti, though it will insu- 

 late a low charge for some time, is a better conductor than shell-lac, glass, and sulphur ; 

 and this conducting power is connected with its readiness in exhibiting the particular 

 effect under consideration. 



1241. Sulphur. — I was anxious to obtain the amount of effect with this substance, 

 first, because it is an excellent insulator, and in that respect would illustrate the re- 

 lation of the effect to the degree of conducting power possessed by the dielectric 

 (1247.) ; and in the next place, that I might obtain that body giving the smallest 

 degree of the effect now under consideration, for the investigation of the question of 

 specific inductive capacity (1277.)' 



1242. With a good hemispherical cup of sulphur cast solid and sound, I obtained 

 the return charge, but only to an amount of 17° or 18°. Thus glass and sulphur. 



