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 - Newton's Theory of Colours, Indicated by Pythagoras and Plato

Chapter 11