slower period, and of greater length, than
those which cause the phenomena of light. From the solar spectrum we
learn that there are a third class of Aether waves, which are of more
rapid vibration, and therefore shorter in length than either the
aetherial heat waves or the aetherial light waves. As already stated,
these are called chemical or actinic waves, because they possess a
greater chemical power than either the heat or the light waves that form
the central part of the spectrum.

Now this question suggests itself to us in relation to these chemical
waves. What are these so-called chemical waves that are produced in the
aetherial medium by the activity and heat of the sun? It must be
remembered that the aetherial waves which give rise to both light and
heat, and also these chemical waves, are first set in motion by the sun,
at least as far as our solar system is concerned. We are perfectly
conversant with the phenomena and characteristics of both heat and
light. We are able to exactly determine what their particular effect
will be on matter, and to describe that effect in a perfectly
straightforward manner. The same, however, cannot be said of these
so-called chemical waves that lie chiefly in the violet and ultra-violet
end of the solar spectrum. What, then, is a chemical wave, its
particular nature, and its exact properties? That we know it can
decompose certain compounds, as Carbonic Acid Gas, CO_2, and so give
rise to chemical decomposition, has been proved by Professor Tyndall and
others, but I have never yet seen any record of any attempt to find out
what these chemical waves are. There may have been such attempts made to
discover their origin and character, but I have not seen any such
record. I purpose, therefore, to offer an explanation as to the
character and origin of these chemical or actinic waves, which I hope to
prove by philosophical reasoning. We have already seen (Arts. 54 and 59)
that both heat and light are convertible, or can be transformed into
electricity, so that the same aetherial wave motion which can produce
light can also produce heat, and that in its turn can produce
electricity. Thus we learn that there is a very close identity between
light, heat, and electricity; indeed it can be demonstrated that the
same aetherial wave motion which produces electricity can produce the
other two.

Lorentz,[14] in an article on "The Identity of Light Vibrations with
Electric Currents," states tha