Experiments and Inductions. 97 



again but reversed, the leaves diverge to 80° positive. Shell-lac 

 cylinder showed the same effect. 



46. A piece of a roll of brimstone 2 inches long, set on end 

 upon the extremity of a cylinder of fine black sealing-wax 2 

 inches in diameter and 15 inches high, and upon top of the roll 

 a B. D. strongly charged positive. In a few minutes the brim- 

 stone was positive all over, and the wax negative. 



The same piece of sulphur was cleaned with soda, rinsed with 

 water, dried in oven, and then set on the wax as before, with 

 charged B. D. on top. In a few minutes it was found to be 

 negative all over, and so was the wax. 



47. The electroscope charged 98° positive. On its top plate 

 was put a small plate of sealing-wax unexcited. The leaves fell 

 to 90°, which continued steady for some minutes. Then took 

 off the cake of wax, and the leaves stood out again to 98° ; and 

 on examining the cake, found that it had acquired a slight nega- 

 tive excitement. 



Suspended Dielectrics. 



48. White silk thread was for the most part used in suspend- 

 ing them. In its ordinary condition it conducts slowly, as the 

 following experiment shows. (See also 17. and 18.) 



a. A brass ball was suspended from a free conductor by a 

 white silk thread 4 feet long. At a distance of about 12 inches 

 below the point of suspension, a brass wire fastened to plate of 

 electroscope pressed against the thread. The ball was now 

 charged, and a few minutes afterwards the gold-leaves began to 

 diverge, and continued to do so slowly. The thread was then 

 heated in a close vessel on sand-bath to about 300° F., then 

 taken out and the ball suspended with it as before. No diver- 

 gence of the leaves ensued, and for two or three hours this per- 

 fect insulating quality was preserved. 



b. While the brass ball was suspended from the high-dried 

 thread an excited cylinder of shell lac is brought close below it, 

 held for ten seconds, then withdrawn. The ball has received no 

 charge ; but if dust is flying about (as when a hassock is beaten 

 close to the ball), it is soon charged with the same electricity 

 as the shell lac. 



c. A brass ball is suspended by the undried silk thread, and a 

 negative-excited cylinder of shell lac is held close below it. The 

 ball becomes charged positive, and the thread negative*. 



* This appears to have been the case in Dr. Faraday's experiments 

 under the heading " Convection or Carrying Discharge " (Experimental 

 Researches, §§ 1562-67). Being unable to understand the reasoning by 

 which phenomena of apparent induction are represented as due to the con- 



Phil Mag. S. 4. Vol. 29. No. 194. Feb. 1865. H 



