24 Prof. Tyndall on the Diamagnetic Force. 
Arr. IV.—On the Diamagnetic Force; by Prof. Tynpsuu.* 
Wiru regard to the character of diamagnetic force great diver- 
sity of opinion prevails. In Germany we have Weber affirming 
that diamagnetic bodies possess a polarity opposed to that of iron. 
Weber’s countryman, Von Feilitsch, combats this opinion in a. 
series of Memoirs recently published in Poggendorff’s ‘Annalen. 
He affirms that diamagnetic bodies possess a polarity the same as 
that of iron; and endeavors to bring the phenomena into har- 
mony with this view. In this country, on the contrary, we have 
Prof. Faraday, and it was believed, Prof. Thomson, neither of 
whom are prepared to admit the existence of any polarity what- 
ever on the part of diamagnetic bodies. These divergences were 
a sufficient proof of the difficulty of the subject, and the neces- 
sity of caution in dealing with a the author, therefore, thought 
it well to commence with the fundamental phenomena, and | 
ascending from them to the more complicated, to endeavor toob- 
tain, by strict adherence to experiment, a clear insight as to the 
real nature of ae: force by which certain bodies are repelled by 
the poles of a net. 
Spee an ate series of experiments made with different 
bodies, and under the most diverse circumstances, the author se- 
lected a few which clearly exhibited the law according to which 
the repulsive force augments when the strength of the repelling 
magnet is increased. Were the repulsion of a diamagnetic body __ 
dependent on any constant property of the mass, then its repul- : 
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sion must be simply proportional to the strength of the magnet; 
but it is proved by the concurrent testimony of experiments car- 
ried on in Germany, France, and England, that, for a wide range 
of magnetic power, the repulsive force increases as the square of 
the strength of the inflnencing magnet. This leads inevitably 
to the conclusion, that the repulsion of a diamagnetic body de- 
pends, not alone on the magnet operating upon it, but upon the 
joint action of the magnet and diamagnet. A piece of bismuth, 
for example, in presence of the magnet is thrown by the Jatter 
into a state of excitement, which varies as the magnetic strength 
varies, and in virtue of which the substance is repelled. ‘The 
next question to be decided is, whether the state of excitement 
evoked by one-pole, ina diamagnetic body, enables a pole of an 
ypposite quality to repel i 4 
- To decide this, two cores of soft iron were so bent, 
two semi-cylindrical ends of the cores could be pl ae 
gether, so as t ia Seite a single. cylinder of the same diameter as 
‘the : coer of the cores The cahoots Ate > 
Pe Pee 1 ig eae 
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