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CHAPTER X
OF ETHER. AND THE WEIGHT AND ELASTICITY OF THE AIR
1. THE moderns understand by ether, a very
rare fluid 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. The existence of such a
fluid is generally acknowledge, although many authors, even among
the moderns, differ about its nature; some supposing it to be
a sort of air, much purer than that which invests our globe; others
maintaining, that it is a substance approaching to that of the
celestial fire, which emanates from the sun and other stars; others
make it generically different from all other matter, and its parts
finer than those of light; alledging, that the exceeding tenuity
of its parts, render 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, by the extreme subtlety
of its parts, it intimately penetrates all bodies, and exerts
its energy every where.
2. But, whatever be the sentiments now entertained
with respect to the existence and nature of ether, we find the
origin of them all in what the ancients have said on this subject.
The Stoics first of all taught, there was a subtile and active
fire, which diffused itself through, and 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, sustained,
preserved, and linked together: for it embraced every thing, and
in it the celestial bodies perform their revolutions.
3. Aristotle, explaining Pythagoras’s
opinion of ether, ascribes the same also to Anaxagoras, saying,
that he looked upon the most remote spaces of the universe, as
filled with a substance, called ether by the philosophers of his
time, but which he himself understood to be a subtile and active
tire. And 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.
4. Pythagoras, according to Diogenes Laertius,
and Hierocles, affirmed, that the air which invests our earth,
is impure and mixed; but that the air which is above, is pure,
healthful, and all of a piece. He calls it free ether, emancipated
from all gross matter, a celestial substance that penetrated at
will the pores of all bodies; just like that of the Newtonians,
which fills all space, without giving any obstruction to the stars
in their courses. And Empedocles, one of the most celebrated disciples
of Pythagoras, is quoted by Plutarch, St. Clemens Alexandrinus,
as admitting an ethereal substance, which filled all space, and
contained in it all the bodies of the Universe.. Likewise Plato,
speaking of air, distinguishes it 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.
5. The nature of air was no less known among
the ancients, than that of ether. They regard it as a general
menstruum, containing all the volatile parts of every thing in
nature, which being variously agitated, and differently combined
in its embrace, produced all that multiplicity of ferments, meteors,
tempests, and all the other changes in it, which we experience.
They were acquainted too with its weight, though the experiments
transmitted to us relative to this are but few. Aristotle appears
to have observed this quality in it, for he speaks of a vessel
filled with air, as weighing more than one quite empty. Plutarch
and Stobceus quote him as teaching that the air in its weight
is between that of fire, and of earth; and be himself’, treating
of respiration, 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 expresses
in the very same terms the sentiments of Asciepiades on this subject,
representing him among other things, as saying, that the external
air by its weight, opened its way with force into the breast.
There is still extant a treatise of Heron of Alexandria, wherein
he constantly applies the elasticity of the air, to produce such
effects, as cannot but convince us, that he perfectly understood
that property of it. And what will appear still more surprising,
is, that Ctesibius, upon the principle of the air’s elasticity,
invented windguns, which we look upon as a modern contrivance.
Philo of byzantium gives us 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. Seneca also
knew its weight, spring, and elasticity; for he describes the
constant effort it makes to expand itself, when it is impresssed;
and affirms, that it has the property of condensing itself, and
forcing its way through all obstacles that oppose its passage.
6. The notions generally received respecting
fire, and its properties, are clearly to be found in Plato, Stoboeus,
Aristotle, and Lucretius; the first of whom says, that fire is
generated of motion, it being the effect of the act and friction
of the small particles of bodies. Aristotle speaks of some philosophers
of his time, who taught, that flame was nothing else, but small
corpuscular parts, continually succeeding one another in rapid
motion ; that fire was composed of pyramidical particles whose
sharp angles stung us in entering our pores, and melted metals,
by discovering their parts, which is what Descartes hath repeated
from him. Demonax affirms, that fire hath weight. Lucretius does
the same; adding, that the reason of its always appearing to tend
upwards, is owing to a foreign cause; to wit, the pressure of
the air, which buoys its flame up, and makes it seem to mount.
Chapter 11
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