QS' PHILOSOPHICAL TRANSACTIONS. ■ [aNNO 1776. 



cular board, of the same dimensions, coated with tin foil, and furnished with a 

 glass handle screwed to, and standing upright on it. These bodies having re- 

 mained in contact some seconds, the board was raised up by the glass handle ; 

 when, applying the knuckle to the tin foil coating, a snap was heard, a spark 

 seen, and a small sensation felt. On replacing the board, and permitting it to 

 remain some seconds, as before, having touched the tin foil with a finger, on 

 removing it again, and applying the knuckle, as at first, the same phenomena 

 were produced ; and might, Mr. Adams observed, be repeated for a long time, 

 without any renewal of the excitation of the wax, any further than the replacing 

 the board might be said to excite it. It immediately occurred that, as this plate 

 of wax, &c. was made by excitation, a strong negative electric, the phenomena 

 produced by it could only be the reverse of those Mr. H. had formerly made 

 with an excited plate of glass, and published in the Phil. Trans., vol. 64, viz. 

 where Mr. H.'s were positive, these were negative ; and where his were nega- 

 tive, these were positive. 



But, to determine this matter, Mr. H. made the following experiments. First, 

 he insulated Mr. Canton's electrometer, and having electrified the balls posi- 

 tively, he presented toward them the excited wax, as soon as it had been sepa- 

 rated from the coated board ; and perceived that the balls were attracted by the 

 wax ; but, if the balls were electrified negatively, they were as plainly repelled 

 by it. The board produced just the contrary effect. Secondly, he held his 

 Leyden vacuum, or analysis of the Leyden bottle, described Phil. Trans., vol. 

 64, by the coated bulb, and touched the brass ball on the neck of it with the 

 coated board, the moment it had been separated from the excited wax, &c. and 

 instantly perceived a variety of beautiful streams dart from the point of the wire 

 in the bottle, and spread themselves in different directions through the bulb. 

 On repeating the experiment, and presenting the coated part of the bottle to- 

 ward the board, a small spark of light appeared on the point of the inclosed 

 wire ; a plain indication that the point had received electricity, and that the 

 coated board, being separated from the wax, &c. was strongly electrified plus ; 

 and consequently the coating of wax, &c. on the plate of glass, minus. These 

 phenomena, being so often produced, without a fresh excitation of the wax, 

 though they are astonishing to strangers, will not be so surprizing to electricians, 

 who have considered Mr. Grey's experiment with a cone of sulphur, contained 

 in a glass vessel, which, as often as they were separated, showed signs of elec- 

 tricity in all states of the weather. See Dr. Priestley's History of Electricity, 

 '2d edit. p. SQ. 



Mr. H. has showed, at large, in a former paper, that merely heating cither 

 glass or amber will not make them electrical ; but the friction of glass against 

 glass, or sealing-wax against sealing-wax, previously warmed, will excite either 



