490 Proceedings of the Royal Society 
to speak, one only of which is utilised, viz., that which takes place 
(fig. 2) when the greatest length of the iron core lies in the line 
joining the two poles ; the other polarity ensues when this main 
axis is perpendicular to the line of poles (fig. 3). This second 
Fig. 2. Fig. 3. 
polarity is, from the less favourable position of the core, necessarily 
weaker than the first; hut it struck me that it might be quite suffi- 
cient to furnish the internal current, leaving to the more powerful 
polarity the task of generating the external current. Another 
advantage seemed to flow from this utilisation. When an armature 
without coil or closed circuit revolves within a magnet, the 
energy expended in its motion heats its particles. When the 
core is provided with a coil and closed circuit, part of this energy, 
instead of assuming the form of heat, is transmuted into the 
energy of an electric current, and the electricity induced is so 
much deducted from the heat that would otherwise appear in the 
armature. In the ordinary construction the weaker polarity, being 
unprovided with a coil, results only in heat ; but if it be furnished 
with such, as in the arrangement I suggest, and its molecular 
energy thereby tapped, so to speak, the heat of the armature may he 
partially withdrawn in the shape of an electric current. A current 
sufficient to magnetise the electro-magnet may thus be got, for no 
additional expenditure of force, hut only by the conversion of heat 
that would otherwise he mere waste, so far as the action of the 
machine was concerned. When one of Wilde’s small machines, in 
which a battery of permanent magnets is used instead of an electro- 
magnet, is turned by the hand, additional resistance is felt on the 
armature circuit being closed more especially by a short wire. The 
current got from the armature would thus seem to be formed 
partially from the conversion just mentioned, and partially from a 
new access of force demanded by the creation of the current. In 
the arrangement I here describe, a different action takes place, for 
when the coil of the electro-magnet is disjoined from the magnetic 
coil and included in the circuit of a single Bunsen cell, the feeling 
