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veloped when its electro-magnet is excited by the current 
from four pint Grove's cells. The electro-magnet of this 
machine is now excited by its own residual magnetism in 
the following manner : — A small magnet cylinder (3*5 inches 
diameter and 14 inches long) is bolted to the top of the 10 
inch cylinder, so that the sides and axis of the former are 
parallel with the similar parts of the latter. The cylinders 
are separated for a space of three-quarters of an inch by 
packings of brass, and consequently act upon each other by 
induction through the intervening space, instead of by con- 
tact as in ordinary methods of magnetisation. 
The residual or permanent magnetism of the large electro- 
magnet with its cylinder is very considerable, being many 
times greater than that of the four small permanent magnets 
with which it was originally excited. 
The small scale upon which the author’s experiments 
have been repeated by physicists has, in some instances, 
given rise to the notion that the residual magnetism of an 
electro-magnet is a lower degree of permanent magnetism 
than that which originally formed the basis of his augmen- 
tations. 
The coils of the small armature are placed in connection 
with those of the great electro-magnet, and when the 
armature is rotated the magnet cylinders act and react 
on each other until the electro-magnet is excited to the 
highest degree of intensity. By this arrangement of the 
armatures and cylinders the minor current for exciting 
the electro-magnet is kept distinct from the major current 
from the large armature, which may be coiled for currents 
of high or low tension, according to the purpose for which 
they are required. 
So far as the author has communicated the results of his 
investigations on the principle of accumulative action in 
electro-dynamics, they have been obtained with machines 
designed with reference to the peculiar form of armature 
