which we have briefly traced, the all-pervading ether constitutes
a sort of unseen world remarkable enough from any point of view,
but to which the theory of our authors ascribes capacities
hitherto unsuspected by science. The very existence of an ocean
of ether enveloping the molecules of material bodies has been
doubted or denied by many eminent physicists, though of course
none have called in question the necessity for some interstellar
medium for the transmission of thermal and luminous vibrations.
This scepticism has been, I think, partially justified by the
many difficulties encompassing the conception, into which,
however, we need not here enter. That light and heat cannot be
conveyed by any of the ordinary sensible forms of matter is
unquestionable. None of the forms of sensible matter can be
imagined sufficiently elastic to propagate wave-motion at the
rate of one hundred and eighty-eight thousand miles per second.
Yet a ray of light is a series of waves, and implies some
substance in which the waves occur. The substance required is one
which seems to possess strangely contradictory properties. It is
commonly regarded as an "ether" or infinitely rare substance;
but, as Professor Jevons observes, we might as well regard it as
an infinitely solid "adamant." "Sir John Herschel has calculated
the amount of force which may be supposed, according to the
undulatory theory of light, to be exerted at each point in space,
and finds it to be 1,148,000,000,000 times the elastic force of
ordinary air at the earth's surface, so that the pressure of the
ether upon a square inch of surface must be about
17,000,000,000,000, or seventeen billions of pounds."[4] Yet at
the same time the resistance offered by the ether to the
planetary motions is too minute to be appreciable. "All our
ordinary notions," says Professor Jevons, "must be laid aside in