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Prof. Tyndall on the Diamagnetie Force. 25 
were of the same or of opposite names. A bar of bismuth was 
freely suspended, so that both poles could act upon it simultane- 
ously. en the cores were excited, so that the poles were 
alike, the bismuth was repelled; when the .poles were of differ- 
ent names, the bismuth bar remained motionless ; all action upon 
it was annulled. This experiment confirms those of Reich, and 
proves that the condition, whatever it may be, which is evoked 
by one magnetic pole is neutralized by the other,—that each par- 
ticular pole evokes a condition peculiar to itself;—and here we 
obtain the first glimpse of the dual nature of the force under 
consideration. 
he next portion of the inquiry treated of the deportment of 
diamagnetic bodies when acted upon, first, by the magnet alone; 
secondly, by the electric current alone; and, thirdly, by the cur- 
rent and the magnet combined. en we speak of the deport- 
ment of bismuth in any one of the cases mentioned, no exact 
meaning can be attached to the phrase unless it be first strictly 
defined in what direction, as to the planes of crystallization, the 
mass has been cut. A bar of bismuth, in which the planes of 
principal cleavage are parallel to the length of the bar, and acted 
upon by the voltaic current alone, will set itself parallel to the 
current’s direction. A bar, on the contrary, in which the planes 
of cleavage are transverse, will set itself at right angles to the 
current’s direction, The former bar Prof. Tyndall calls a normal 
diamagnetic bar; the latter an abnormal one. The most perfect 
antithesis is observed in all cases between the deportment of the 
normal diamagnetic bar and a bar of soft iron; the forces which 
cause a deflexion of the former from right to left produce a defiex- 
ion of the latter from left to right. If the former take up a po- 
sition of equilibrium from southwest to northeast the position 
taken by the latter will be from southeast to northwest; a 
throughout all the experiments the same opposition of action 
is exhibited. By mechanical means, an abnormal magnetic bar 
and diamagnetic bodies in the magnetic field; but the thing 
which chiefly concerns us is the strong presumption which the 
voked in magnetic bodies by the action of currents, or magnets, 
or of both combined, to an influence, of the same nature but an- 
Szoonp Serres, Vol. XIX, No. 55.—Jan., 1855. 4 
