'Photoheliometer' definitions:

Definition of 'Photoheliometer'

From: GCIDE

Photoheliometer \Pho`to*he`li*om"e*ter\, n. [Photo- + heliometer.] (Astron.) A double-lens instrument for measuring slight variations of the sun's diameter by photography, utilizing the common chord of two overlapping images. [Webster 1913 Suppl.]