[f. Gr. ἀκτῖν- ray + -ISM.]
† 1. ‘The radiation of heat or light, or that branch of Philosophy which treats of it.’ Craig, 1847. Obs.
2. That property or force in the sun’s rays by which chemical changes are produced, as in photography.
1844. R. Hunt, Brit. Assoc. Report, 30. By a most careful prismatic analysis of the rays … I have ascertained the relative quantity of the active chemical principle (Actinism).
1849. Lindley, Elem. Bot., 56. Mr. Hunt believes that the germination of seeds in the spring … is dependent upon the variations in the amount of actinism—or chemical influence—of light and of heat in the solar beam.
1862. R. H. Patterson, Ess. Hist. & Art, 13. The electro-positive and electro-negative rays, of which Heat and Actinism are the representatives.
