n. [ Gr. &unr_;, &unr_;, ray + -meter ] (a) An instrument for measuring the direct heating power of the sun's rays. (b) An instrument for measuring the actinic effect of rays of light. [ 1913 Webster ]
n. [ Gr. &unr_; power + E. actinometer. ] An instrument for measuring the intensity of the photogenic (light-producing) rays, and computing the power of object glasses. [ 1913 Webster ]