124 Prof. Barlow’s Account of Experiments on the Magnetism 
of the plate, whichever pole of the needle was directed to the 
former. The needle, of course, therefore, deviated different 
ways (all other things being the same), when it was above or 
below the axis ; but in the direct horizontal line of the axis, no 
motion in the needle took place. 
11. The above are the principal experiments that I assisted 
in making by revolving the plate ; but these having suggested 
to Mr Barlow, that all the results obtained might be explained, 
by supposing, that there existed a slight magnetic power in cop- 
per, and in the various metals which had a tendency to 
draw the needle after the plate, or the latter after the former, 
he endeavoured to exhibit this by direct experiment, independent 
of revolution. With this view, he neutralized a needle very ac- 
curately ; and then applying very near to its poles the end of a 
round brass ruler, the attraction of the latter was obvious, — it 
drew the needle several degrees, — then, withdrawing it, and 
catching the needle again in its returning vibration, it was drawn 
out some farther degrees, and, in a very short time, the deflec- 
tion was converted into a revolution, which, by alternately pre- 
senting and withdrawing the needle, was at length rendered very 
rapid. 
12. The same result was obtained by two or three different 
pieces of brass ; but there were other pieces, although of the 
same size and form, which had little or no effect. 
The following experiment is due to Mr Sturgeon of Wool- 
wich. 
13. A thin copper plate or wheel, about five or six inches in 
diameter, was suspended very delicately on an axis, and then 
one side a little weighted, in order to give it a tendency to os- 
cillate. The heavy point was now raised level with the axis, 
and the number of vibrations the plate made before it came to 
rest were counted. The same was again done, with this diffe- 
rence only, that the vibrations now took place between the poles 
of a horse-shoe magnet ; and the number of them before the 
plate come to rest, was very little more than one-half of what 
they were in the former instance. 
This is the converse of M. Arago’s experiments, in which he 
shews the effect of copper and other metallic rings, in diminish- 
ing the number of oscillations of a magnetic needle. 
