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An instrument devised originally for measuring the diameter of the sun; now employed for delicate measurements of the distance and relative direction of two stars too far apart to be easily measured in the field of view of an ordinary telescope.

A double-lens instrument for measuring slight variations of the sun's diameter by photography, utilizing the common chord of two overlapping images.

An instrument for measuring the direct heating effect of the sun's rays.

Of or pertaining to the heliometer, or to heliometry.

ractice of measuring the diameters of heavenly bodies, their relative distances, etc. See Heliometer.

s micrometer, and when the instrument is large and equatorially mounted, it is known as a heliometer. -- Double refraction micrometer, a species of double image micrometer, in which the two images are formed by the double refraction of rock crystal. -- Filar, or Bifilar, micrometer. See under Bifilar. -- Micrometer…