520 The Source of Electric Energy . [September, 
finitely, or until reduced by resistance to heat. Such is the 
case in light transmission. Its conductor is infinitely ex- 
tended. Its movement is therefore continuous, and light 
transmission can only cease by its gradual conversion into 
heat, or into some other mode of motion. Yet it is not 
difficult to produce a condition of radiant adtion somewhat 
similar to that existing in a charged eleCtric condudtor. For 
if we have a closed room bounded by reflecting surfaces, and 
with a source of light in its centre, there is no evidence of 
the accumulation of this light, however perfect the reflection 
may be. Each increment of the light may suffer a series of 
reflections, but these are instantaneous, and every successive 
portion of light emitted immediately ceases to be visible. 
When the light is quenched, or the light-yielding chemical 
aCtion hindered, the light instantly disappears. What has 
become of it? It has not escaped from the room. It has 
not sunk into the wall. It has only partly been converted 
into static heat. Where is the remainder ? Energy cannot 
die out. It must continue to exist in some form. If not 
light, or heat, or mass motion, what is this form of energy ? 
May it not exist in a condition resembling static electricity ? 
It is possible that the induced light energies of the interior 
substance of the room may be neutralised, like the induced 
eleCtric energies within a charged conductor. The vanished 
energy may exist on the surfaces of the room precisely as 
static electricity exists on the surface of a conductor. No 
trace of this energy could possibly be discovered from the 
interior, on account of the interior neutralisation, on the 
same principle that prevents our finding electricity in the 
interior of a charged conductor. Nor is it possible for us to 
test it from without the surface, as we can electricity. There 
are some possible phenomena in this connection which we 
cannot discover. There is no evidence of a movement of 
light force when the surface of a room thus charged is in- 
creased by opening it into another dark room. But the 
aCtion here is an induction, not a current, and would not be 
likely to affeCt the eye. Nor can we perceive any trace of 
outward induction of this energy through the confining walls. 
And yet it is not quite illogical to argue that light and elec- 
tricity are like modes of motion, and that the reason we 
cannot discover every phenomenon of the one in the other 
is simply because we cannot subject them to the same pro- 
cesses of investigation. 
If there really exists such a similarity between light radi- 
ation and eleCtric radiation, the aCtion of light would not 
resemble the movement of an eleCtric current through the 
