EXPERIMENTS ON ELECTRICITY. 1 S9 



flap is rubbed by the revolving glafs cylinder it is brought into 

 dole contact ; and the electricity adhering more forcibly to the 

 glafs, is carried forward into the open air, which air not hav- 

 ing been rendered negative like the filk, does not counter- 

 balance the furface of the glafs, and therefore its capacity 

 being leffened, it emits the charge it hadjuft. abforbed. And 

 he thinks the amalgamated cufhion affifls the procefs, by bring- 

 ing a furface of a conducting quality, and in connection with 

 the earth into clofer contact. 



The experiments of Mr. Cavallo were made by letting fub- Cavallo's expe- 

 fiances fall out of his hand for the mofi part upon an infulated trici a fj- or d e d " 

 plate of tin, whence they were (hook off upon a table, or upon by the fall of 

 a chair ; from which he again took the fubftance up, and let it SJjfjfjJj^-Jj 

 fall upon the tin plate to the number of times required. After plate, 

 thefe reiterations he applied his tin plate to the plate of his 

 multiplier. In his experiments a piece of zinc little more 

 than half an ounce, was dropped ten times fucceffively upon 

 the plate, which lair, as appeared by the fubfequent opera- 

 tions of the multiplier, was electrified negatively. Another 

 piece dropped ten times produced the fame effect. Zinc was 

 heated to 110 degrees, and one repetition of the experiment 

 produced the fame effect, but ftronger. A fhilling, an half 

 crown, a new guinea, a piece of copper, a piece of malleable 

 platina, with like manipulation, produced fimilar effects, but 

 differing in degree. Platina produced very little electricity; 

 but when heated it was found to produce an effect contrary to 

 the preceding ; that is to fay, it electrified the tin plate pofi- 

 tively. A piece of lead appeared to produce negative elec- 

 tricity in the tin ; but when hot pofitive. A piece of iron af- 

 forded very equivocal refults. A piece of grain tin afforded 

 negative electricity, as well when heated as when cold. — 

 When the cold tin was dropped from a pair Of iron tongs, and 

 let fall from the tin plate upon a chair, whence it was picked 

 up by means of the fame iron tongs, it produced weak pofitive 

 electricity. Tin when heated afforded electricity of the fame 

 quality, but greater in quantity. Mr. Cavallo alternately 

 ufed the hand and the iron tongs with refults generally like 

 the preceding, that is to fay, negative electricity in the tin 

 plate, when the grain tin was dropped from the hand, and 

 pofitive when it fell from the tongs. Bifmuth produced pofi- 

 tive electricity ; but when the bifmuth was made very hot, 



the 



