Definition of "æther"

I ſuppose this æther pervades all groſs bodies, but yet ſo as to ſtand rarer in their pores than in free ſpaces, and ſo much the rarer, as their pores are leſs. And this I ſuppose (with others) to be the cauſe, why light incident on thoſe bodies is refracted towards the perpendicular; […] I ſuppose the rarer æther within bodies, and then denſer without them, not to be terminated in a mathematical ſuperficies, but to grow gradually into one another; […]

1679 February 28, Thomas Birch, quoting Isaac Newton, “The Life of the Honourable Robert Boyle. [Letter from Isaac Newton to Robert Boyle.]”, in Robert Boyle, The Works of the Honourable Robert Boyle. In Five Volumes. To which is Prefixed the Life of the Author, volume I, London: Printed for A[ndrew] Millar, […], published 1744, page 70

On Wings the Birds through Æther glide, / And Fiſhes cut with Fins the Tide.

1746 February 28, Criticus [pseudonym], “Dialogue on Women”, in [Mark Akenside], editor, The Museum: Or, The Literary and Historical Register, volume II, number XXV, London: Printed for R[obert] Dodsley […], page 389

Having ſhewn how the Æther cauſes a great part of the Phænomena of Nature, it may be aſked, whence thi general material Cauſe has its great Activity and Power? […] This Cauſe muſt be either Matter or Spirit, there being nothing in the Univerſe, which we know if, beſides theſe two. But this Cauſe cannot be Matter: for Matter is in own Nature inert, and has not any Activity in itſelf; and conſequently cannot communicate any Power to the Æther. And therefore the Cauſe, which gives the Æther its Activity and Power, muſt be Spirit. Spirit, which intercedes the Particles of Æther, and gives them a repulſive Power, and ordains and executes the Laws, by which Æther and Bodies act mutually on one another, muſt be preſent in all Parts of Space, where there is Æther.

1747, Bryan Robinson, A Dissertation on the Æther of Sir Isaac Newton, London: Printed for Charles Hitch […]; quoted in “Literary Memoirs. A Dissertation on the Æther of Sir Isaac Newton, by Bryan Robinson, M.D. London, Printed for Charles Hitch, at the Red Lion in Pater-noster-Row, 1747. Containing 140 Pages in Octavo, Exclusive of a Short Preface.”, in The Museum: Or, The Literary and Historical Register, volume III, number XXVIII, London: Printed for R[obert] Dodsley […], 11 April 1747, pages 59–60

But the moſt valuable Qualities of the ÆTHER are it's medicinal ones; it having been found by repeated Experience to be an excellent Remedy in moſt nervous Diſeaſes; particularly in Fits of all ſorts, whether Epileptic, Convulſive, Hyſteric, Hypochondriac, or Paralytic: […]

1759, M[atthew] Turner, An Account of the Extraordinary Medicinal Fluid, Called Æther, [Liverpool]: Printed by John Sadler, page 5

The whole matter of the univerſe may be divided into atoms and æther. […] The latter, æther, is a ſubtile elaſtic fluid, whoſe particles have a continual tendency to ſeparate or fly off every way, unleſs impreſſed by ſome body: This æther ſurrounds each atom like an atmoſphere, and preſſes equally towards the center of each.

1770 November 1, “Investigator” [pseudonym], “Of the Causes of Attraction and Repulsion”, in Sylvanus Urban [pseudonym; Edward Cave], editor, The Gentleman’s Magazine, and Historical Chronicle, volume XL, London: Printed […], for D[avid] Henry; and sold by F[rancis] Newbery […], page 497, column 1

The luminous æther of his life was not obſcured by any ſhade dark enough to be denominated a defect.

1793, “[Characters.] An Account of the Late Earl of Mansfield.”, in The Annual Register, or A View of the History, Politics, and Literature, volume XXXV, London: Printed, by assignment from the executors of the late Mr. James Dodsley, for W. Otridge and Son; [et al.], page 274, column 2

M. Malaguti finds that dry chlorine, while acting in the dark upon oxacid æthers, always attacks, and in a uniform manner, the sulphuric æther which is the base of them. […] The action of potash on the compound chloridized æthers is also constant and uniform: the results are always chloride of potassium, acetate of potash, and an organic salt with a base of potash, the acid of which is that which existed in the compound chloridized æther.

1838 March, “Action of Chlorine on Æthers”, in David Brewster, Richard Taylor, Richard Phillips, editors, The London and Edinburgh Philosophical Magazine and Journal of Science, volume XII (3rd Series), number 74, London: Printed by R[ichard] and J[ohn] E[dward] Taylor, […], page 297

[…] I allude to the æthers formed by the union of fatty acids with different alcohols. […] With regard to the fatty æthers themselves, I prepared them generally by M. Berthelot's method, by heating the alcohol and the acid for a day at 392°F. in a tube hermetically sealed; the product was mixed with a little æther, and it was digested some time with slaked lime in the water-bath, to separate the free acid from the neutral compound.

1858 October 15, M. Hanhart, “On Some New Æthers of Stearic and Margaric Acids”, in William Francis, editor, The Chemical Gazette, or, Journal of Practical Chemistry, in All Its Applications to Pharmacy, Arts and Manufactures, volume XVI, number CCCLXXXIV, London: Published by Taylor and Francis, […], page 384