sa 



Sir H. Davy on a 



Fig. I. Fig. 5. 



[Jan. 



Fig. 1 is the regular primary crystal resting on one of its 

 planes, and having its solid angles truncated. 



P on P' 109° 28' 



P on« 125 16 



Fig. 2 is the more common shape of the secondary crystals, 

 resulting from a disproportionate extension of some of their 

 planes. 



Article III. 



On a new Phenomenon of Electromagnetism, By Sir Humphry 

 Davy, Bart. Pres. RS.* 



O* a subject so obscure as electromagnetism, and connected 

 by analogies more or less distinct with the doctrines of heat, 

 light, electricity, and chemical attraction, it is not difficult to 

 frame hypotheses ; but the science is in a state too near its 

 infancy to expect the developewent of any satisfactory theory ; 

 and its progress can only be ensured by new facts and experi- 

 ments, which may prepare the way for extensive and general 

 reasonings upon its principles. Influenced by this opinion, I 

 am induced to lay before the Society an account of an electro- 

 magnetic phenomenon I observed about fifteen months ago in 

 the laboratory of the Royal Institution, and which I have lately 

 had an occasion of witnessing in a more perfect manner, through 

 the kindness of Mr. Pepys, by the use of a large battery, con- 

 structed under his directions for the London Institution, and 

 containing a pair of plates of about 200 square feet. In describ- 

 ing this phenomenon, I shall not enter into very minute details, 

 because the experiments, which led to the discovery of it, are 

 very simple, and, (hough more distinct with a large apparatus, 

 vet it may be observed by the use of a pair of plates containing 

 from ton to fifteen square feet. 



Immediately after Mr. Faraday had published his ingenious 



♦ From the Philosophical Transactions for 1823, Part II, 



