argosies venturing on its limitless expanse.

There remains the question of the luminiferous ether by whose agency
the waves of light are borne through space. The ether is as mysterious
as gravitation. With regard to ether we only infer its existence from
the effects which we ascribe to it. Evidently the ether must extend as
far as the most distant visible stars. But does it continue on
indefinitely in outer space? If it does, then the invisibility of the
other systems must be due to their distance diminishing the quantity
of light that comes from them below the limit of perceptibility, or to
the interposition of absorbing media; if it does not, then the reason
why we cannot see them is owing to the absence of a means of
conveyance for the light waves, as the lack of an interplanetary
atmosphere prevents us from hearing the thunder of sun-spots. (It is
interesting to recall that Mr Edison was once credited with the
intention to construct a gigantic microphone which should render the
roar of sun-spots audible by transforming the electric vibrations into
sound-waves). On this supposition each starry system would be
enveloped in its own globule of ether, and no light could cross from
one to another. But the probability is that both the ether and
gravitation are ubiquitous, and that all the stellar systems are
immersed in the former like clouds of phosphorescent organisms in the
sea.

So astronomy carries the mind from height to greater height. Men were
long in accepting the proofs of the relative insignificance of the
earth; they were more quickly convinced of the comparative littleness
of the solar system; and now the evidence assails their reason that
what they had regarded as the universe is only one mote gleaming in
the sunbeams of Infinity.