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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- 

 mao-net 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 hio-h or low tension, according to the purpose for which 

 they are required. 



So far as the author has communicated the results of his 

 investio-ations on the principle of accumulative action in 

 electro-dynamics, they have been obtained with machines 

 desioTied with reference to the peculiar form of armature 



