ACTIN'OGRAPH ( Gk. nitric, akt is, ray + ypa etc, graphcia, to write). An instrument for recording automatically the chemical effects of radiations from any source, especially the sun. Formerly the actinic or chemical, the visual or optic, and the thermal or heat rays were spoken of as the components of a beam of sunshine as though all kinds of rays were bound up therein. But we now know that the sun radiates an immense ,variety of so-called waves or rays of different wave-lengths and that appar ently any one of these waves may produce chem ical, visual, or thermal effects, and perhaps elec trical, depending upon the molecular nature of the object that it strikes. Thus the same wave that produces a special blue light in the solar spectrum will produce a little heat if it fall upon a delicate thermometer. or a great effect resulting in intense heat and light if it fall upon a proper mixture of chlorine and hydrogen or other chemicals. It is no longer proper to speak
of the snit's. actinic rays. hut of actinic effects of the solar radiation. The simplest forms of aetinograph are those that expose standard photographic plates or films ( iodides, chlorides, or bromides of Aver) to the sun's action for short, definite periods of time. Those that util ize the action of sunshine to cause the union of chlorine and hydrogen (Draper's and Bunsen's), or the precipitation of gold from a solution of the chloride of gold and oxalic acid, or the evolution of oxalic acid from a solution of ferric oxalate and chloride of iron require complex measuring arrangements that do not easily lend themselves to graphic. self-registration.