Calorific rays

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the invisible, heating rays which emanate from the sun, and from burning and heated bodies.

See also: Calorific

Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
References in periodicals archive ?
Thus did Herschel prove the existence of invisible forms of light, which he called "calorific rays." Further experiments showed that "calorific rays" could be reflected, refracted, absorbed, and transmitted in the same way as visible light.