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platinum wire about nine inches in length, which wire 
immediately became white-hot, and as suddenly ceased to 
be visibly hot until contact with the branch wires had been 
broken for a short time and afterwards re-established. 
This momentary ignition of the platinum wire appeared 
to Mr. Wilde to be due to the diversion of the greater portion 
of the current generated by the armature into the new 
channel or short circuit established by the platinum wire 
through the armature coils, before the high degree of mag- 
netism which had been maintained in the electro-magnet by 
the full current from the armature had been reduced by the 
loss of a portion of the current so diverted. 
The results obtained by Siemens and Wheatstone are 
undoubtedly very interesting from a scientific point of view, 
but, practically, the exciting of the electro-magnet by the 
current from the armature used in connection with it, pro- 
duces results very inferior to what are obtained from similar 
machines, the electro-magnets of which are excited by a 
separate source of electricity of small power, as, in the latter 
case, the full force of the current generated by the armature 
coil is available for the performance of external work. 
Mr. Wilde having himself, some time ago, made some 
experiments similar to those of M. Siemens and Dr. Wheat- 
stone, came to the conclusion that in the present state of our 
electrical knowledge, the difficulty of utilising the current 
from the armature after it had passed through the coils of 
the electro-magnet was insuperable; as it is absolutely 
necessary that the coils of the electro-magnets of electro- 
magnetic machines, when excited by intermittent currents? 
should be of considerable length, in order that they may 
acquire and retain a charge of electricity or magnetism, as 
has been shown by Drs. Henry and Faraday in their experi- 
ments on the induction of a current upon itself. On the 
other hand, for the production of powerful electro-dynamic 
effects, it is necessary that the wire of the armature coil 
