What is a double-lens instrument for measuring slight variations of the sun's diameter by photography, utilizing the common chord of two overlapping images called?
photoheliometer — A double-lens instrument for measuring slight variations of the sun's diameter by photography, utilizing the common chord of two overlapping images. (Webster's 1913.)
Sources
- Webster's Unabridged Dictionary, 1913 edition (public domain, via GCIDE / Project Gutenberg).
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- Published: 2026-07-17T00:00:00-07:00 · Modified: 2026-07-17T00:00:00-07:00