By _ether_ the moderns understand a rare fluid, or species of matter,
beyond the atmosphere, and penetrating it, infinitely more subtile than
the air we respire, of an immense extent, filling all the spaces where
the celestial bodies roll, yet making no sensible resistance to their
motions. Some suppose it to be a sort of air, much purer than that which
invests our globe; others, that its nature approaches to that of the
celestial fire, which emanates from the sun and other stars; others,
again, suppose it to be generically different from all other matter,
_sui generis_, and its parts finer than those of light; alleging that
the exceeding tenuity of its parts renders it capable of that vast
expansive force, which is the source of all that pressure and dilatation
whence most of the phenomena in nature arise; for that by the extreme
subtilty of its parts it intimately penetrates all bodies, and exerts
its energy everywhere. This last is the opinion of Newton and Locke. But
whatever be the sentiments now entertained on the subject, we find the
origin of all of them in the ancients.
The stoics taught, that there was a subtile and active fire which
pervaded the whole universe, that by the energy of this ethereal
substance, to which they gave the name of ether, all the parts of nature
were produced, preserved, and linked together; that it embraced every
thing; and that in it the celestial bodies performed their revolutions.
According to Diogenes Laertius and Hierocles, Pythagoras affirmed, that
the air which invests our earth is impure and mixed; but that the air
above it is essentially pure and healthful. He calls it “free ether,
emancipated from all gross matter, a celestial substance that fills all
space, and penetrates at will the pores of all bodies.”
Aristotle, explaining Pythagoras’s opinion of ether, ascribes the same
also to Anaxagoras. Aristotle himself, in another place, understands by
ether, _a fifth element pure and unalterable, of an active and vital
nature, but entirely different from air and fire_.
Empedocles, one of the most celebrated disciples of Pythagoras, is
quoted by Plutarch, and St. Clemens Alexandrinus, as admitting an
ethereal substance, which filled all space, and contained in it all the
bodies of the universe, and which he calls by the names of Titan and
Jupiter.
Plato distinguishes air into two kinds, the one gross and filled with
vapours, which is what we breathe; the other “more refined, called
ether, in which the celestial bodies are immerged, and where they roll.”
The nature of _air_ was not less known to the ancients than that of
ether. They regarded it as a general “_menstruum_,” containing all the
volatile parts of every thing in nature, which being variously agitated,
and differently combined, produced meteors, tempests, and all the other
changes we experience. They also were acquainted with its weight, though
the experiments transmitted to us, relative to this, are but few.
Aristotle speaks of “a vessel filled with air as weighing more than one
quite empty.” Treating of respiration, he reports the opinion of
Empedocles, who ascribes the cause of it “to the weight of the air,
which by its pressure insinuates itself with force” into the lungs.
Plutarch, in the same terms, expresses the sentiments of Asclepiades. He
represents him, among other things, as saying, that “the external air by
its weight opens its way with force into the breast.” Heron of
Alexandria ascribes effects to the elasticity of the air, which show
that he perfectly understood that property of it.
Seneca also knew its weight, spring, and elasticity. He describes “the
constant effort it makes to expand itself when it is compressed;” and he
affirms, that “it has the property of condensing itself, and forcing its
way through all obstacles that oppose its passage.”
It is still more surprising, however, that Ctesibius, “upon the
principle of the air’s elasticity,” invented _Wind-guns_, which we look
upon as a modern contrivance. Philo of Byzantium gives a very full and
exact description of that curious machine, planned upon the property of
the air’s being capable of condensation, and so constructed as to manage
and direct the force of that element, in such a manner as to carry
stones with rapidity to the greatest distance.
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