The New Student's Reference Work/Actinism

Ac′tinism (Gr. aktin, a ray), the chemical property of light, solar or other radiant energy, as the sun’s rays in photography, and by which chemical changes are produced. The sun-recording instrument which measures and records the quantity of actinism present is called the actinograph; while the actinometer is the instrument or apparatus for measuring the chemical effects of radiation from any source, as in measuring the intensity of the rays on a photographic plate, or piece of sensitized paper, when exposed to the sunlight.