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 haye 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, which has been excited, continues 
to attract its keeper even when the current is cut off. 
His researches extended to— 
