56 Proceedings of Philosophical Societies. [Jan. 



and the change of variation was accurately demonstrated by 

 Prof. Gellibrand, of Gresham College, in 1635. 



In 1600, Dr. Gilbert, of Colciiester, published, in Latin, his 

 Treatise de Magneie " In this truly philosophical and original 

 work, the author endeavours to prove that the phajnomena of 

 magnetism are owing to the magnetic polarity of the earth, — 

 that soft iron becomes a temporary magnet Oy the influence of 

 the earth, — that in steel the magnetic property is induced by the 

 same cause, \vith more difficulty indeed, but the effect is more 

 permanent; and he explains the motion of the needle, and the 

 powers of common magnets, by showing that opposite poles of 

 different magnets attract each other in some definite ratio of 

 their distance. He indulges, which could hardly be avoided in 

 that age, in some vague hypotheses, and details some futile 

 experiments ; but notwithstanding this, his views display very 

 extraordinary powers of mind ; and though censured by his 

 contemporary. Lord Bacon, for endeavouring to solve the phseno- 

 meua of gravitation by magnetic attraction, yet his researches 

 have a character of inductive reasoning perfectly in the spirit of 

 the philosophy of that great Pian, who, had he studied his work 

 with more attention, would have found in it numerous examples 

 of his own sublime method of pursuing science, a contempt for 

 the speculative authority of the ancients, and an appeal, almost 

 new in those times, to the laborious method of repeated experi- 

 ments." 



The President then went on to mention the discovery of the 

 diurnal variation of the needle in 1722 by George Graham; the 

 labours of Lambert, Coulomb, and Robison on the laws that 

 regulate magnetic attractions and repulsions, and the mathema- 

 tical views of the theory of magnetism brought forward by 

 Epinus and Robison on the hypothesis of a single magnetic 

 fluid, and the recent memoirs of M. l-'oisson on the supposition 

 of two fluids, an Austral and Boreal, presented to the Royal 

 Academy of Sciences of Paris. 



" The hypothesis of magnetic, which so closely agrees 

 with that of electric fluids, has been defended by similar 

 arguments, and illustrated by analogous experiments ; and the 

 connexion between these two classes of phaenomena had been 

 often observed and dwelt upon by philosophers." Beccaria 

 supposed the magnetism of the earth to be produced by electric 

 currents, and similar opinions were advanced and supported by 

 vague analogies, and insufficient facts ; but " till the important 

 discovery of M. Qirsted, the true relations of magnetism and 

 electricity were unknown." " I could with pleasure," said the 

 President, " dwell on this discovery, and its immediate conse- 

 quences in the developement of new and extraordinary results ; 

 and would the time allotted to a discourse of this nature allow 

 it, I should have great satisfaction in describing to you the 



