Dictionary entry

Heliometer

Webster's Dictionary 1913

He′li‐om″e‐ter (?), n. [Helio- + -meter: cf. F. héliomètre.] (Astron.) 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.