C 347 ;] 
XVI. On the Magnetism of Iro?i arising from its rotation. By 
Samuel Hunter Christie, Esq, M. A. of Trinity College^ 
Cambridge ; Fellow of the Cambridge Philosophical Society ; 
of the Royal Military Academy . Communicated April 20, 1 825, 
by J. F. W. Herschel, Esq. Sec. R. S. 
Read May 12, 1825. 
A s the principles on which phasnomena depend can only 
be discovered by a careful investigation of the circumstances 
attending every new fact which presents itself, its import- 
ance must not, in the first instance, be estimated by the 
magnitude of the effects produced, but by their peculiarity. 
However minute may be the effects, an inquiry into the laws 
which govern them, if unattended by any other, will have 
this advantage, that these laws will serve as an additional 
test of the correctness of the principles advanced for the ex- 
planation of the more striking phaenomena, firmly establish- 
ing their truth, if the consequences of those principles, or 
being incompatible with them, pointing out their fallacy. 
Thus the severest test that the principle of gravitation has 
been subjected to, is the explanation of the minute irregula- 
rities in the planetary motions ; and the coincidence of the 
observed irregularities with those deduced from the applica- 
tion of this principle would have established its truth beyond 
dispute, had any doubt previously remained. In the expe- 
riments which I am about to detail, the effects produced are 
of this minute character ; but as they point out a species of 
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