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THE APPLICATIONS OF PHYSICAL FORCES. [BOOK v. 



A large machine of this construction, exhibited some years ago at 

 the Polytechnic Institution in London, was capable of igniting a short 

 platinum wire. 



Siemens' armature was happily applied by Wilde, in 1866, to the 

 construction of a machine of extraordinary power. When the machine 

 was in full action it melted a rod of iron 15 inches in length and a 

 quarter of an inch in diameter, and gave the most brilliant illuminating 

 effects when the discharge took place between carbon points. As nearly 

 as could be estimated, the mechanical force absorbed in producing these 

 results was from eight to ten-horse power. Wilde's machines have 

 been successfully employed by Messrs. Elkington for the precipitation 

 of copper and other metals, and he has lately proposed some important 

 modifications to adapt them to the production of the electric light. 



Fra. 432. Pacinotti's machine (plan). 



Some years before Wilde's experiments were published, Holmes 

 had constructed on the Saxton principle a powerful magneto-electric 

 machine, which has been successfully used at Dungeness and other 

 lighthouses, and machines differing little from Holmes's are employed 

 in some of the French lighthouses. In Holmes's original machine 

 forty-eight pairs of compound bar-magnets were arranged for the 

 armatures (160 in number) to revolve between the poles of the magnets, 

 and by a system of commutators the current was obtained always in 

 the same direction. French engines on this principle have been recently 

 constructed by a commercial company, the Alliance, which has 



