æthrioscope

[Lat. aethra; Gr. αἰθρία (uri a) = fine weather, the open sky; and σκοπέω ( skopco ) = to behold.] An instrument devised by Sir John Leslie, and designed to determine the radiation against the sky. It consisted of two gla bulbs united by a vertical gla tube so narrow that a little column of liquid was supported in the tube by its own adhesion. The lower bulb was protected by a metallic envelope, and gave the temperature of the air, whilst the upper one was blackened, and was surrounded by a metallic cap, designed to protect the bulb from terrestrial radiation. "The sensibility of the instrument," says its inventor, "is very striking, for the liquor ince antly falls and rises in the stem with every pa ing cloud." (See Tyndall on Heat, 3rd ed., 1868, p. 367.)