repetition oj M, Arago's experiments on magnetism, &c. 477 
directions. The truth of this proposition, it is no less evi- 
dent, is independent of the axis of suspension, which may 
pass through a part of the system any how ‘situated with re- 
spect to the magnets, in virtue of the property of a magnet 
whose force to turn a system of which it makes a part, round 
a fixed centre, is the same wherever in the system it is 
placed, and the same as if it were in the centre. 
Hence it follows, that if two equal and similar magnets be 
laid parallel to each other, but in a reversed position on a 
horizontal glass plate freely suspended by a thread, the sys- 
tem will be devoid of any polar tendency, ( which we shall 
express by calling such a system neutral). It is difficult 
however to procure two magnets exactly equal, and of equal 
force. But fortunately this is of no consequence, as a slight 
deviation from perfect neutrality may be corrected by inclin- 
, ing the stronger needle a little more or less to the plane of 
the plate. In fact the proposition is general ; and by a 
proper adjustment of the positions of two magnets however 
unequal, with respect to the axis and to each other, they may 
be made to neutralize each other. 
15. As this adjustment however is nice, and as magnets 
influence each other, and our object moreover called for the 
utmost delicacy, we adopted a more refined application of the 
principle just detailed. A circular glass disc was prepared, 
8 inches in diameter, and suspended by three silk threads 
from a filament of silk, descending along the axis of a copper 
tube about 5 feet long, passing wdth stiff friction through 
collars in the cieling of the apartment, and serving nicely 
by means of an index to regulate the height of the glass 
disc. 
