e host of
erroneous conceptions which at once arise at the introduction of this
luckless term. This notion of an "imaginary ether" should be at once and
forever discarded by every writer on physics. The very word should be
remorselessly expunged from every discussion of the subject. It is one
of the most baneful words in the whole dictionary of scientific
terminology. It stands for a fiction as useless as it is without
foundation. It is useless because superfluous, and not needed in order
to account for the phenomena. An ether is no more necessary in the case
of light than it is in the case of sound. Thermal vibrations are the
oscillations of atoms, not the undulations of an ether. If it be urged
that rays of light and heat will traverse a vacuum, we reply, that the
much-derided aphorism, "Nature abhors a vacuum," is as true at this day
as it was before Torricelli's experiment. A perfect vacuum has never
been produced; and if it were to be produced, the ether must be
excluded, else it would be no vacuum, after all. For, if there were such
a thing as an ether, it must of course be some form of matter; nobody
ever claimed for it the character of motion or force. If it be
considered as matter, then, we are confronted with new difficulties; for
all matter must exert gravitation. Weight is our sole test of the very
existence of matter; it is the balance which has proved that nothing
ever disappears. Imponderable matter is no more possible than a
triangular ellipse. Away, then, with such a mischief-breeding
conception! Let this last-surviving fetich be ousted from the fair
temple of inorganic science. Undulations have been measured and counted;
quantitative relations, like those expressed in Joule's law, have been
established between them; but an "ether" has never yet been the object
of human ken.

We have expressed ourselves thus emphatically upon this all-important
point, in order to warn the reader of Dr. Youmans's book against drawing
conclusions which the author himself evidently does not mean to convey.
No clear ideas can ever be entertained in physics until this anomalous
"ether" is excommunicated; and therefore we wish it had been banished
from this excellent treatise. We differ also very widely from the
author's views of animal heat, but have not space to enter upon the
discussion. With these exceptions we know of nothing in the work that
could be improved. It is an honor to American science, and fully merits
a more