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heliometer|hiːlɪˈɒmɪtə(r)|
[ad. F. héliomètre (1747 in Hatz.-Darm.), f. helio- + Gr. µέτρον measure, -meter.]
1. An astronomical instrument originally devised for measuring the diameter of the sun; now much used in determining the angular distance between two stars. Also attrib.
It consists of a telescope, having the object-glass divided into two parts, each of which can be made to slide past the other and thus superpose the two images produced.
1753Short in Phil. Trans. XLVIII. 165 M. Bouguer had read..in the year 1748, a memoir, in which he describes an heliometer; which is an instrument, consisting of two objective glasses, for measuring the diameters of the planets. 1836Penny Cycl. V. 269 An invention of his in 1748, which he calls the heliometer, and which is in fact the first double object glass micrometer, and was properly so called. 1874Monthly Not. R. Astron. Soc. XXXIV. 279 The planet Juno at the opposition of 1874 appears to be very favourably situated for a trial of this method..and the Repsold Heliometer, with which the transit is to be observed, a suitable instrument. 1893Sir R. Ball Story of Sun 334 The heliometer of six inches aperture at the Yale Observatory. 1893D. Gill (title) Heliometer observations for determination of stellar parallax made at the Royal Observatory, Cape of Good Hope. 1905Astrophysical Jrnl. XXII. 103 The heliometer measures made in connection with transits of Venus in 1874 and 1882.
†2. Name given to a complex form of portable sun-dial, used for ascertaining solar time, latitude, length of day, times of sunrise and sunset, etc. Obs.
1875Knight Dict. Mech.
So heliometry |hiːlɪˈɒmɪtrɪ|, the art or practice of using the heliometer. |