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VIII. On the mutual action of the particles of magnetic bodies, 
and on the law of variation of the magnetic forces generated at 
different distances during rotation. By S. H. Christie, Esq. 
M. A. F. R. S. 
Read February 15 and 22, 1826. 
In my Letter to Mr. Herschel, published in the Transactions, 
I communicated the results of some experiments which I had 
made, with the view of determining according to what law 
of distance the magnetism developed in copper and other 
metals during rotation, varied. I was aware, that all I could 
offer at that time must be considered as distant approxima- 
tions towards useful results ; but as I had witnessed several 
of the very interesting experiments in which Mr. Herschel 
and Mr. Babbage were engaged, I was desirous that they 
should be in possession of whatever results I had obtained. 
In these experiments, I had made use of a thick copper plate 
revolving under a magnetized needle, and of magnets revolv- 
ing under a copper disc ; so that, at different distances, some 
of the forces which were brought into action during rotation, 
had very different angles of inclination to the plane of the 
needle, in the one case, and to the plane of the disc in the 
other ; and in consequence of this, the results were by no 
means uniform. In order to remedy this, I proposed, instead 
of a disc, to make use of a copper ring, as, in this case, the 
poles of the magnet revolving vertically under it, no lateral 
forces would be called into action ; and I expected that the 
