170 An Account of some Electro-Magnetic Experiments 
times 87°, according to its sensibility. It is quite remarkable, 
that, in this case, the deviation of the needle is the reverse from 
what it would have been if the heat of a lamp had been applied. 
From the 6th experiment it is clear that it would have been to 
the east ; whilst, by using sulphuric acid and water, it is to the 
west, when the end turned to the south is dipped in the fluid. 
The chemical action between the acid and the metals, indepen- 
dently of the heat evolved, having such a powerful influence on 
the results of the experiment, it was deemed necessary to inquire 
whether one metal, with an acid to act upon it, would produce 
the deviation. With this view, a trial was first made with a 
metal and an acid, not strongly acting on each other. 
10. A slip of copper, perhaps 16 or 18 inches long, was then 
bent, as in Fig. 12., and the ends coiled up, and brought as close 
into contact as possible ; the whole being, as usual, disposed in 
the magnetic meridian, the needle being inside the copper, and the 
coil to the south. If sulphuric acid is added to the water in the 
cup, there is no deviation of the needle perceptible. But then, if a 
bar of zinc be immersed in the fluid, and made to touch the cop- 
per, the needle deviates 10° or 12° eastward. 
11. If, instead of sulphuric acid, nitric be employed, a devia- 
tion of the needle to the west is observable, as soon as the acid 
is added to the Tvater. 
12. The bent slip was now made of zinc, in the same manner 
as it was made of copper in Fig. 12., as in the former experi- 
ment. The coil being turned to the south, and sulphuric acid 
poured into the cup, the effect was very strange. The needle, 
placed as in Fig. 12., first deviated to the east , but soon after 
turned to the west. In that situation it remained for some mi- 
nutes, and then gradually returned to the magnetic meridian. 
If a new quantity of acid be added to the fluid, a subsequent 
deviation is produced, the needle first turning eastward and af- 
terwards westward. Whilst this deviation took place, a bar of 
copper was introduced into the fluid, and made to touch the jzinc. 
The needle began irregularly to vacillate, and actually was 
made to turn round several times on its axis. 
13. The same experiment was repeated, but the ends of the 
zinc were made so as not to touch each other, as in Fig. 13. As 
soon as the acid is added, there is a slight deviation to the east, 
