14 Mr. Kemp onthe Simple and 
- plate was now gradually lowered in the jar, and the deviation pro« 
duced on the needle became greater ; and as it continued to ap- 
proach the plate of zinc, it gradually increased until at the dis- 
tance of about the thirty-second of an inch, which was as near as 
the inequalities of their surfaces would allow the plates to be 
brought: the deviation of the needle amounted to nearly 75°, 
The copper plate was now gradually raised in the jar, and the 
deviation produced on the needle decreased just in preportion as 
the distance between the plates became greater; so that when it 
arrived at the surface of the liquid, the needle stood at the same 
point as it did when it was first immersed. 
ExpEeRiIment II.—In this experiment the relative situations of 
the plates were reversed ; the copper plate being placed at the bot- 
tom of the jar and the zinc plate lowered into it. The effect pro- 
duced on the needle was precisely the same as in the former expe« 
riment. | 
Both of the plates had a few perforations made in them to allow 
the passage of the hydrogen from their under surfaces up through 
the liquid, and thus keep them in the most favourable state for 
the action of the liquid. When the plates were immersed in a 
wooden trough, eighteen inches long, in a horizontal position, the 
very same effects were produced upon the needle, as the distance 
of the plates was varied. 
ExPERIMENT IJI.—Having procured a wooden box, fifteen 
inches square, and two feet in length, rendered tight by cement, a 
plate of copper and one of zinc was cut fifteen inches square, so as 
to be easily immersed and taken out of the box; to each of the 
plates a strong copper wire was soldered. The box was then filled 
with a strong solution of muriatic acid and water, and a very fine 
iron wire, about four inches in length, was then attached to the 
extremity of each of the wires proceeding from the plates, so as to 
form a continuous metallic communication between the two plates. 
The plates were then immersed into the box, the copper at one ex« 
tremity and the zine at the other, having two feet of liquid inter- 
posed between them. At the instant of immersion, a violent action 
took place on the zinc plate, yet the centre of the thin iron wire 
scarcely attained a heat equal to 212° of Fahrenheit. As, how- 
ever, the plates were made gradually to approach each other, the 
heat increased, and when at a distance of one foot from each other, 
the centre of it began to assume a red heat, and as the distance be- 
came less, the heat augmented, until, when about the sixteenth of 
an inch from each other, nearly the whole length of iron wire was 
heated to redness. 
The effect produced on the thin iron wire, will be more apparent, 
if at the different distances the plates are taken out, washed, and 
again immersed ; as the numerous globules of hydrogen, which at- 
tach themselves to the surfaces of the plates, are thus disengaged, 
