ate action of light, with which we are physical action resulting inchaciges the jefly concerned in photography,
matter struck by light, changes which sometimes are physical only and somotimes chemical, but very often of such a nature that it is very difficult to ascertain how much of the effect is due to physical and how much to chemical change. I may mention some examples of physical changes produced by light. Orystalline selenium, a rare non-metallic element, analogons to sulphur, becomes a much better conductor when the conductivity mun ling cin the ight falls upon i
Text read from the printed page and cleaned; old type leaves the occasional error.