382 
The Source of Electric Energy . [July, 
rays we receive are transmitted by the air, not by the ether ; 
and that, therefore, we know only the range of atmospheric 
transparency. There may be etherial rays which are 
reflected at the surface of our atmosphere, and which fail to 
penetrate to us. As for solid and liquid substances, some 
are transparent to this whole range, some to a portion of it 
only, and some opaque to the whole. But these latter may 
be transparent to some other range of vibrations, possibly of 
lower pitch than those of light and radiant heat. The highly 
opaque metals, for instance, may be transparent to a range 
of vibrations to which air and the other transparents to light 
are completely opaque. And it is not impossible that such 
a range of vibrations constitutes eledtric energy, for it is a 
well known fadt that all good eledtric condudtors are highly 
opaque to etherial radiation, and that the most of trans- 
parent solids are good insolators of eledtricity. Some 
transparent liquids, however, condudt eledtricity imperfedtly ; 
but this would only show a wide range of transparency in 
these liquids. 
There is another fadt, of some importance in this connec- 
tion, which it will be well to mention before proceeding. This 
is the fadt that all the best transparents to light are colour- 
less. There are but few transparents which possess colour, 
and the transparency of these is imperfedt. Opaque substances, 
on the contrary, are usually of strongly declared colour. 
Some of them refledt all the light rays, and are white in hue. 
Others absorb a portion of the rays, and are of some special 
shade of colour. Others, again, absorb all the rays, and are 
black. Are there not some peculiar relations revealed in 
this diversity of behaviour to light ? Two sets of substances 
resist absorption of light, the colourless and the white. Of 
these the first set is transparent. It condudts light. The 
other set is opaque. It resists light in every sense, and 
repels it through the air. Of coloured substances some 
absorb more, some less, of the light rays ; some refledt the 
unabsorbed portion, others partly transmit it. And, finally, 
the transmission of light through the best transparents is 
only partial. In all of them it is partly converted into 
heat. 
These fadts are singularly paralleled by certain fadts in 
eledtrical behaviour. To eledtricity, as to light, certain 
substances are transparent, others opaque. But the best 
transparents, or condudtors, absorb a portion of the eledtric 
current and convert it into heat. Poor condudtors absorb a 
considerable portion of the current. They resemble the 
coloured transparents to light, or translucent substances. 
