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IV. On the Transmit Magnetic State of which various Substances are suscep- 
tible. By William Snow Harris, Esq. Communicated by Davies Gilbert, 
Esq. F.P.R.S. 
Read June 17, 1830. 
i. The influence of bodies, not permanently magnetic, on the compass needle, 
has led to some further researches in magnetism of singular importance. The 
valuable papers of M. Arago and other eminent philosophers on this subject, 
communicated to the Royal Academy of Sciences, together with those of our 
no less talented countrymen which have appeared in the Royal Society’s Trans- 
actions, are calculated to excite a deep interest in physics. In presenting to 
the Royal Society, after such valuable contributions to science, an account of 
some inquiries which I have myself been led to make in this branch of natural 
knowledge, T am encouraged by the belief, that whilst the deductions are for 
the most part derived from simple and direct experiments, the investigation 
has been carried on under new conditions ; and that although some facts already 
made known, have been again referred to, it will nevertheless be found to con- 
tain results of sufficient consequence to render it not unworthy of notice. 
I have been particularly led to persevere in this investigation, at various 
times, from having observed (Edinburgh Journal of Science, vol. v. p. 325.) 
that the reciprocal action of a rotating metallic disc, and a magnetic bar, is 
not considered by M. Arago as the result of any magnetism induced in the 
disc, but is attributed by him to some new force as yet undiscovered : — and 
also, from the circumstance, that the magnetic susceptibility of non-metallic 
bodies, seems not to have been in many instances satisfactorily established: — 
two inquiries of considerable importance. 
2. When these researches were first commenced*, a curious effect was ob- 
served, evidently resulting from vibration, which it may be of consequence to 
mention. 
A thin circular ring of copper of about half an inch wide, ten inches in 
* In 1826. 
K 2 
