127 
Most of the before-mentioned experiments were varied 
by using an electropeter, which enabled me very rapidly 
to discontinue and renew, and also to change the direction 
of the current exciting the electro-magnet ; but without 
obtaining any results worthy of particular description, in 
addition to those already stated; as reversing the voltaic 
current did not produce effects on the suspended disc 
essentially different from what would have been exhibited 
by the discontinuance and immediate renewal of the cur- 
rent in the same direction. 
The arrangements of the battery were also varied by 
using six pairs of elements of zinc and platinised silver, 
each having about 1.5 inches acting surface, in addition 
to the four cells of nitric acid battery, so arranged that 
when the more powerful current of the latter was discon- 
tinued, a comparatively feeble current continued in some 
instances in the same, and at other times in the reverse 
direction. These arrangements did not, however, give any 
particular results, further than that the effects, on dis- 
continuing the powerful current, were perhaps somewhat 
diminished ; showing that the freedom of the electro- 
magnet from residual magnetism is only of slight importance 
in dia-magnetic experiments, and that the motions produced 
on the suspended disc are due to the exaltation or depression 
of the magnetic force, and not to its entire cessation. 
I also repeated some of the experiments of Professor 
Oerstead, an account of which was recently published in the 
Philosophical Magazine for 1849, vol. xxxiv. p. 81, in which 
he pointed out that when the polar pieces are brought very 
closely together, and a small bar of dia-magnetic substance 
is suspended immediately over the space separating the 
polar pieces, the suspended bar may assume either the 
equatorial or the axial direction. I found this the case 
with bars of various metals ; and that these would take 
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