-1859] 



WRITINGS OF JOSEPH HENRY. 



355 



of paper surrounding 

 the cylinder. This in- 

 strument, which is 

 very sensitive, has 

 been modified and im- 

 proved by Dellman. 



On the top of the 

 flat roof of his house 

 Peltier placed a flight 

 of steps by which he 

 could ascend holding 

 in his hand an ordi- 

 nary gold-leaf electro- 

 scope armed with a 

 comparatively large 

 sized polished ball. 

 The ball of the elec- 

 troscope was held at 

 the height say of four 

 ■^^°- ■^'^- feet above the roof of 



the house, and in this position it was touched by the end 

 of a wire connected with the earth below. It thus formed 

 the termination of a perpendicular conductor, and was 

 of course negatively electrified — the bulb more intensely 

 than the leaves below, but the stratum of air in which it was 

 placed being in the same state it exhibited no signs of elec- 

 tricity. It was then elevated by ascending the steps to the 

 height of six feet above, and held by the lower plate. The 

 leaves in this case diverged with negative electricity, because 

 the ball was still farther removed from the earth, and the 

 attraction being lessened, the part of the electricity in the 

 leaves was set free and ascended to the bulb by repulsion, 

 leaving a deficiency in the leaves. When the electroscope 

 was brought down to its first position the leaves again col- 

 lapsed since there was again an equilibrium ; and when the 

 electroscope was depressed below its normal position the 

 leaves became positively electrified by the increased attrac- 

 tion of the earth, and in this way the electroscope was 



