S56 Mr. Faraday's Researches in Electricity. {Series XL) 



It will be unnecessai'y to describe the steps of the investigation 

 minutely; I will at once proceed to the simplest mode of 

 proving the facts, first in air and then in other insulating 

 media. 



1218. A cylinder of solid shell-lac, 0-9 of an inch in dia- 

 meter and seven inches in length, was fixed upright in a 

 wooden foot (fig. 3.) : it was made concave or cupped at its 

 upper extremity so that a brass ball or other small arrange- 

 ment could stand upon it. The upper half of the stem having 

 been excited negatively by friction with warm flannel, a brass 

 ball, B, 1 inch in diameter, was placed on the top, and then 

 the whole arrangement examined by the carrier ball and 

 Coulomb's electrometer (1180. &c.). For this purpose the 

 balls of the electrometer were charged positively to about 360°, 

 and then the carrier being applied to various parts of the ball 

 B, the two were uninsulated whilst in contact or in position, 

 then insulated*, separated, and the charge of the carrier ex- 

 amined as to its nature and force. Its electricity was always 

 positive, and its force at the different positions a, b, c, d, &c. 

 (fig. 3. and 4.) observed in succession, was as follows : 



at « above 1000° 



b it was 149 



c 270 



d 512 



b 130 



1219. To comprehend the fijll force of these 

 results, it must first be understood, that all 

 the charges of the ball B and the carrier are 

 charges by induction, from the action of the 

 excited surface of the shell-lac cylinder; for 

 whatever electricity the ball B received by 

 communication from the shell-lac,either in the 

 first instance or afterwards, was removed by 

 the uninsulating contacts, only that due to in- 

 duction remaining; and this is shown by the 

 charges taken from the ball in this its uninsu- 

 lated state being always positive, or of the 



contrary character to the electricity of the shell-lac. In the 

 next place the charges at a, r, and d were of such a nature as 



* It can hardly be necessary for me to say here, that whatever general 

 state the carrier ball acquired in any place where it was uninsulated and 

 then insulated, it retained on removal from that place, notwithstanding 

 that it might pass through other places, that would have given to it, if un- 

 insulated, a different condition. 



