Editorial Note
The entry below ran as two installments of an alphabetical reference feature serialized weekly in this newspaper, drawing almost verbatim on Ephraim Chambers’ Cyclopaedia (1728). Aether was not fringe or occult in 1729. It was the standard, textbook explanation for what fills space, taught to a general newspaper audience and debated seriously by Newton and the Cartesians alike. We’ve joined the two weekly installments into one continuous piece, preserving original wording and spelling.
ÆTHER is usually understood of a thin, subtile Matter, or Medium, much finer and rarer than Air; which commencing from the Limits of our Atmosphere, possesses the whole Heavenly Space.
The Word is Greek, supposed to be form’d from the Verb aithein, to burn, to flame; some of the Ancients, particularly Anaxagoras, supposing it of the Nature of Fire.
The Philosophers cannot conceive that the largest Part of the Creation should be perfectly void; and therefore fill it with a Species of Matter under the Denomination of Æther.— But they vary extremely as to the Nature and Characters of this Æther. Some conceive it as a Body sui generis, of its own Kind, appointed only to fill up the Vacuities between the heavenly Bodies; and therefore confined to the Regions above our Atmosphere. Others suppose it of so subtile and penetrating a Nature, as to pervade the Air, and other Bodies; and possess the Pores and Intervals thereof. Others deny the Existence of such specifick Matter; and think the Air it self, by that immense Tenuity and Expansion it is found capable of, may diffuse it self thro’ the interstellar Spaces, and be the only Matter found therein.
In Effect, Æther being no Object of our Sense, but the mere Work of Imagination, brought only upon the Stage for the Sake of Hypothesis, or to solve some Phænomenon real or imaginary, Authors take the Liberty to modify it how they please. Some suppose it of an elementary Nature, like other Bodies, and only distinguish’d by its Tenuity, and the other Affections consequent thereon; which is the Philosophical Æther. Others will have it of another Species, and not Elementary; but rather a sort of Fifth Element, of a purer, more refined, and spirituous Nature than the Substances about our Earth; and void of the common Affections thereof, as Gravity, &c. The heavenly Spaces being the supposed Region or Residence of a more exalted Class of Beings; the Medium must be more exalted in Proportion. Such is the antient and popular Idea of Æther, or Æthereal Matter.
The Term Æther being thus embarrass’d with a Variety of Ideas, and arbitrarily applied to so many different Things; the later and severer Philosophers chuse to set it aside: and in lieu thereof, substitute other more determinate ones.
Thus the Cartesians use the Term Materia Subtilis, which is their Æther: And Sir I. Newton, sometimes a subtile spirit, as in the Close of his Principia, and sometimes a subtile or Æthereal Medium, as in his Opticks.
The Truth is, there are abundance of Considerations, which seem to evince the Existence of some Matter in the Air, much finer than the Air it self. There is an unknown something, which remains behind, when the Air is taken away, as appears from certain Effects which we see produced in vacuo. Heat, Sir I. Newton observes, is communicated thro’ a Vacuum, almost as readily as thro’ Air: But such Communication cannot be without some interjacent Body, to act as a Medium. And such Body must be subtile enough to penetrate the pores of Glass; and may be very well concluded to permeate those of all other Bodies; and consequently be diffused thro’ all the Parts of Space; which answers to the full Character of an Æther.
The Existence of such Æthereal Medium being settled, that Author proceeds to its Properties; inferring it to be not only rarer and more fluid than Air, but exceedingly more elastick, and active: In Virtue of which Properties, he shews that a great Part of the Phænomena of Nature may be produced by it. To the Weight, e.g. of this Medium, he attributes Gravitation, or the Weight of all other Bodies; and to its Elasticity, the elastick Force of the Air, and of nervous Fibres, and the Emission, Refraction, Reflection, and other Phænomena of Light; as also, Sensation, Muscular Motion, &c. In fine, this same Matter seems the primum mobile, the first Source or Spring of physical Action in the modern System.
The Cartesian Æther is supposed not only to pervade, but adequately to fill all the Vacuities of Bodies; and thus to make an absolute Plenum or Fulness in the Universe.
But Sir I. Newton overturns this Opinion, from divers Considerations; by shewing that the Celestial spaces are void of all sensible Resistance: For hence it follows, that the Matter contained therein, must be immensely rare, in regard the Resistance of Bodies is chiefly as their Density; so that if the Heavens were thus adequately fill’d with a Medium or Matter how subtile soever, they would resist the Motion of the Planets and Comets much more than Quicksilver or Gold.
Transcribed from The Universal Instructor in all Arts and Sciences: and Pennsylvania Gazette, No. XXIV (April 5, 1729) and No. XXV (April 12, 1729).
