Electric Energy in Voltaic Circuits. 493 
folds itself round the circuit, and sends part of one of the pre- 
viously investing paths to the inside, where it displaces part of 
one of the original inside paths, which at once begins to close 
up. Fig. 2 shows it half closed, on the hypothesis of absolute 
suddenness. Fig. 3 the same thing, on the supposition that 
energy possesses something like inertia. The induced current 
is produced by energy flowing along the semi-displaced path 
through the copper. If the change of field stops, fig. 2 is 
supposed quickly to revert to fig. 1, with an opposite trans- 
ference of energy. Three stages in the change of field are 
shown in fig. 4: or this figure may be regarded as showing 
three lines in a uniform field disturbed by a moving con- 
ductor. 
The arrows are drawn as if the energy flowed right away 
again without loss, or at least without complete loss. It is 
easy to reverse one of the arrows, so as to make energy flow 
up from both sides to the secondary circuit; but it is not easy 
to see how energy can reach the copper and be dissipated 
when its path does not pierce the copper atall. The lines 
have to be thought of as first embracing the circuit, then as 
moving away, having left a portion enclosing the circuit be- 
hind, and finally, more lines having come on, as sinking into 
and through the copper, and shutting themselves up ; and so 
on perpetually, as long as the field is changing. The energy 
thus reaches the secondary circuit a little behindhand always, 
which is not wrong. [If all the energy is dissipated in the act 
of passing through the copper, arrows ought not to be drawn 
on the inside paths which are shutting up ; because though 
they are still paths for energy, it does not follow that they are 
made use of; in fact, they cannot be, if all the energy is extinct. 
Probably, however, what all these diagrams better represent 
is the steady state of a field disturbed by the presence of a 
perfect conductor in which there is no dissipation whatever— 
a conductor like the molecules postulated in Ampére’s and 
Weber’s theory of magnetism and diamagnetism. 
Voltaic Energy-paths. (Plate IV.) 
Returning to the Plate showing voltaic-energy path: the 
diagram seems to me to constitute the most absolute and 
complete reconciliation between the truth in the opposing 
views of the voltaic circuit. 
It not only justifies modern voltaic experimenters in their 
recognition of the slope of air-potential near a junction, 
but it partially justifies even the view of old Volta that this 
Phil. Mag. 8. 5. Vol. 19. No. 121. June 1885. 2 L 
