evanescent

Disappearing, vanishing.

He cannot ſuppreſs his diſapprobation […] of thoſe evaneſcent echoes of ſchool philoſophy, faint-warbling through the grove of letters, to the injury of natural and ſcientific knowledge, and the annoyance of English literature.

The sea was each little bird's great playmate. […] In their airy flutterings, they seemed to rest on the evanescent spray.

Disappearing, vanishing.

Consequently, the electromagnetic fields have plane-wave characteristics in local regions, except immediately adjacent to a caustic where there is a rapid transition from the wavelike behavior of the local plane-wave fields to the evanescent behavior beyond the ray path.

The analyte directly affects the optical properties of a waveguide, such as evanescent waves (electromagnetic waves generated in the medium outside the optical waveguide when light is reflected from within) or surface plasmons (resonances induced by an evanescent wave in a thin film deposited on a waveguide surface).

Disappearing, vanishing.

[…] I choſe rather to reduce the demonſtrations of the following propoſitions to the firſt and laſt ſums and ratio's of naſcent and evaneſcent quantities, that is, to the limits of thoſe ſums and ratio's; […] Perhaps it may be objected, that there is no ultimate proportion of evaneſcent quantities; becauſe the proportion, before the quantities have vaniſhed, is not the ultimate, and when they are vaniſhed, is none. […] [B]y the ultimate ratio of evaneſcent quantities is to be underſtood the ratio of the quantities, not before they vaniſh, nor afterwards, but with which they vaniſh.

And what are theſe Fluxions? The Velocities of evaneſcent Increments? And what are theſe ſame evaneſcent Increments? They are neither finite Quantities, nor Quantities infinitely ſmall, nor yet nothing. May we not call them the Ghoſts of departed Quantities?

Barely there; almost imperceptible.

If the Fluids moving in an Evaneſcent Artery [i.e., a capillary] appear Globular, I ſuppose its becauſe the Canal is round, which alters the Caſe much.

Here are Sholes and Sholes, of various Characters, and of the moſt diverſified Sizes; from the gigantic Whale, whoſe flouncings "tempeſt the Ocean," to the evaneſcent Anchovy, whoſe Subſtance diſſolves in the ſmalleſt Fircaſſee.

Ephemeral, fleeting, momentary.

It is to be obſerved, farther, that when we annihilate any thing in our Mind, we conſider it as ſomething evaneſcent, and removed out of Sight; […]

But alas! how momentary was the bliss!—the evaneſcent viſion ſoon fled, and the youthful queen [Mary, Queen of Scots] was arrayed in the melancholy garb of widowhood!