VOL. LXXIX.] PHILOSOPHICAL TRANSACTIONS. 601 



face in contact with the cushion, as indicated by the brush figure. These made 

 the cylinder ring, as if struck with a bundle of small twigs. They seem to have 

 arisen from part of the electricity of the cylinder taking the form of a charge. 



12. With a view to determine what happens in the inside of the cylinder, re- 

 course was had to a plate machine. One cushion was applied with its silken flap. 

 The plate was 9 inches in diameter and -^ of an inch thick. During the exci- 

 tation, the surface opposite the cushion strongly attracted electricity, which it 

 gave out when it arrived opposite the extremity of the flap. So that a continual 

 stream of electricity passed through an insulated metallic bow terminating in 

 balls, which were opposed, the one to the surface opposite the extremity of the 

 silk, and the other opposite the cushion; the former ball showing positive, and 

 the latter negative signs. The knobs of 2 jars being substituted in the place of 

 these balls, the jar, applied to the surface opposed to the cushion, was charged 

 negatively, and the other positively. This disposition of the back surface 

 seemed, by a few trials, to be weaker the stronger the action of the cushion, as 

 judged by the electricity on the cushion side. — Hence it follows, that the inter- 

 nal surface of a cylinder is so far from being disposed to give out electricity during 

 the friction by which the external surface acquires it, that it even greedily at- 

 tracts it. 



13. A plate of glass was applied to the revolving plate, and thrust under the 

 cushion in such a manner as to supply the place of the silk flap. It rendered 

 the electricity stronger, and appears to be an improvement of the plate machine ; 

 to be admitted if there were not essential objections against the machine itself. 



14. Two cushions were then applied on the opposite surfaces with their silk 

 flaps, so as to clasp the plate between them. The electricity was received from 

 both by applying the finger and thumb to the opposite surfaces of the plate. 

 When the finger was advanced a little towards its correspondent cushion, so that 

 its distance was less than between the thumb and its cushion, the finger received 

 strong electricity, and the thumb none; and, contrariwise, if the thumb were 

 advanced beyond the finger, it received all the electricity, and none passed to 

 the finger. This electricity was not stronger than was produced by the good 

 action of one cushion applied singly. 



15. The cushion in experiment 12 gave most electricity when the back sur- 

 face was supplied, provided that surface was suffered to retain its electricity till 

 the rubbed surface had given out its electricity. 



From the last 2 paragraphs it appears, that no advantage is gained by rubbing 

 both surfaces; but that a well managed friction on one surface will accumulate 

 as much electricity as the present methods of excitation seem capable of collect- 

 ing; but that when the excitation is weak, on account of the electric matter not 

 passing with sufficient facility to the rubbed surface, the friction enables the op- 



\0L. XVI. 4 H 



