An Elementary Treatise On Phototopographic Methods And Instruments PDF Download

Excerpt from An Elementary Treatise on Phototopographic Methods and Instruments: Including a Concise Review of Executed Phototopographic Surveys and of Publications on This Subject Light-rays, in addition to their heating and illuminating qualities, have a chemical or so-called "actinic" power, characterized by a general tendency to decompose certain chemical compounds, some of which, for that very reason, being utilized in photography. The term photography, composed of two Greek words phos, or phota, and grapho, means light-drawing or sun-picture, and a photograph may be defined as a picture produced by the actinic action of light-rays (emanating from the object to be pictured) upon a surface chemically prepared for this particular purpose. Although the origin of photography may be ascribed to the alchemists of the sixteenth century, who had observed that chloride of silver becomes blackened when subjected sufficiently long to the action of light-rays, still, photography as we know that art to-day is not so very old. In 1777 the Swedish chemist Scheele discovered that the intensity of the actinic power of light-rays changed with the quality of the light, inasmuch as argentic chloride would turn black quicker when exposed to the rays of the violet end of the solar spectrum. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.