63 
ably diminished; but an inconvenient residuum of heat 
still remained when the machines were worked continuously 
for a long time, such as to render it desirable to adopt some 
means for abstracting the heat more rapidly. 
By means of a current of water, circulating in the hollow 
brass segments which form part of the magnet-cylinder, 
Mr. Chas. E. Ryder, the skilful manager at the works of 
Messrs. Elkington & Co., has happily succeeded in so far 
reducing this heating as to permit of the machines being 
worked, for days and nights together, without intermission, 
and without any sensible diminution of the power of the 
current. 
The author has already shown, elsewhere, that the current 
from a small magneto-electric, or electro-magnetic machine 
is sufficient to excite the electro-magnet of a very large 
machine : and it has been further found, by Mr. G. C. 
Lowe, that the current from one small machine is sufficient 
to excite, simultaneously, the electro-magnets of several 
small machines. In a number of 3J-inch machines which 
have been constructed, under the author’s direction, for 
Messrs Elkington and Co., for the electro-deposition of 
copper on a large scale, the currents from two 3 J -inch 
electro-magnetic machines are made to excite the electro- 
magnets of twenty similar-sized machines to a degree suffi- 
cient to bring out the maximum dynamic effect of each 
machine. 
The electro-magnets of the two 3 J-inch exciting machines 
are charged by the current from a small magneto-electric 
machine ; but the author has found that nearly as good a 
result maybe obtained from the 20 machines, by dispensing 
with the small magneto-electric machine, and employing the 
residual magnetism of the two 3J-inch exciting machines, 
in a manner similar to that described almost simultaneously 
by Mr. Farmer, Messrs. Yarley, Mr. Siemens, and Sir 
Charles Wheatstone. 
