remarkable increase of all the effects, accompanied by a diminution in
the resistance of the machine, is observed when a cross wire is placed
so as to divert a great portion of the current from the electro-magnet,"
had led the lecturer to an investigation read before the Royal Society
on the 4th of March, 1880, in which it was shown that by augmenting the
resistance upon the electro-magnets 100 fold, valuable effects could be
realized, as illustrated graphically by means of a diagram. The most
important of these results consisted in this, that the electromotive
force produced in a "shunt-wound machine," as it was called, increased
with the external resistance, whereby the great fluctuations formerly
inseparable from electric arc lighting could be obviated, and thus,
by the double means of exciting the electro-magnets, still greater
uniformity of current was attainable.

The conditions upon which the working of a well conceived dynamo machine
must depend were next alluded to, and it was demonstrated that when
losses by unnecessary wire resistance, by Foucault currents, and by
induced currents in the rotating armature were avoided, as much as 90
per cent., or even more, of the power communicated to the machine was
realized in the form of electric energy, and that _vice versa_ the
reconversion of electric into mechanical energy could be accomplished
with similarly small loss. Thus, by means of two machines at a moderate
distance apart, nearly 80 per cent, of the power imparted to one machine
could be again yielded in the mechanical form by the second, leaving
out of consideration frictional losses, which latter need not be
great, considering that a dynamo machine had only one moving part
well balanced, and was acted upon along its entire circumference by
propelling force. Jacobi had proved, many years ago, that the maximum
efficiency of a magneto-electric engine was obtained when