310 



shock or other inconvenience of any kind was experienced by 

 the inmates of the house, with the exception of the consterna- 

 tion produced by the deafening sound of the stroke. 



The President suggested that the blackening of the wall 

 may have been produced by the combustion of the wire, and 

 its dissipation in the form of the black oxide of copper. 



The President gave an account of some experiments made 

 by him in electro-magnetism. 



The discovery of the electro-magnet induced hopes that it 

 might be advantageously employed as a moving power, and 

 numerous attempts to effect this have been made. But though 

 probably it cannot be used economically for this purpose, yet 

 many cases occur where cost is but a secondary consideration, 

 and where an electro-magnetic machine would be highly conve- 

 nient. In reference to them, his friend, Mr. Bergin, had endea- 

 voured to construct one suited to the wants of the laboratory or 

 workshop, and in the course of his experiments had consulted 

 Dr. Robinson as to the conditions of current helices, &c, which 

 would produce a given power with least expenditure of bat- 

 tery materials. On these heads he was surprised to find how 

 little is known, and commenced experimenting to instruct 

 himself, and he offers the results which he found, as useful to 

 the practical magnetician, but still more (which was his chief 

 object in pursuing them so far) as offering useful data to those 

 who, like Professor William Thomson, of Glasgow, are en- 

 gaged in investigating the theory of magnetic induction. 



Without intending to enter on that theory, he pointed out 

 the conditions of electro-magnetic excitation, indicated the 

 existence of the coercive force in iron, and explained its agency 

 in producing the permanent magnetism, and another state, 

 which he terms residual excitation, — that, namely, in virtue 

 of which an electro-magnet, Avhich has been excited, continues 

 to attract its keeper even when the current is cut off. 



His researches extended to — 



