Searchlights and Signal Lights: For the Instruction of Officers and Personnel Connected With Searchlights (Classic Reprint)

ISBN-10: 1332193994
ISBN-13: 9781332193998
Category: Technology & Engineering
Pages: 286
Language: English
Published: 2015-08-05

Description

Excerpt from Searchlights and Signal Lights: For the Instruction of Officers and Personnel Connected With Searchlights The first use of any light projector which could be called a searchlight in any sense of the word was on board a Union warship blockading a southern port during the Civil War. On a dark night a Confederate ship attempted to run the blockade, thinking herself secure against detection on account of the blackness of the night. Suspicion, however, was aroused on board the Union ship and the first searchlight used at sea was brought into use. From the Union ship there came a feeble, poorly reflected, widely divergent beam of light. It swung around, searching for the enemy, and finally, faintly illuminated, he was discovered. Crude as was this searchlight, it made a place in warfare for the projector which has since been developed to a remarkable degree of efficiency. This first searchlight was merely a "limelight" produced by playing an oxy-hydrogen flame on a candle of calcium oxide, this source of light being backed by a crude, spherical, polished metal mirror which absorbed about 50 percent of the total light. Shortly after this came the first arc light, which, when used with small, spherical metal mirrors, was useful up to a maximum range of perhaps 300 yards. The next military use of searchlights was at the siege of Paris (1870-71) in which arc lights were used. They burned vertically and the entire arc and flame was used as the source of light, rather than using, as is the present practice, only the very brilliant positive crater. The arc current was about 10 amperes. This light was mounted behind a rather expensive and complicated system of lenses and prisms invented by Fresnel. It had previously found application in lighthouses, and because of the good results obtained by this system in that service, it was tried on searchlights. However, on account of its complication, expense, and low efficiency, it could not stand in the face of later inventions. In 1876, Col. Mangin brought out his silvered glass reflector which gave excellent results and was the forerunner of modern searchlight mirrors. For a long time it had been recognized that a parabolic silvered glass mirror would be the best reflector obtainable, but at that time it was impossible to grind one. Spherical mirrors were useless because of unavoidable distortion of the beam. Mangin's reflector consisted of a mirror with its front surface and back surface spherical, but with different radii and not concentric. This corrected spherical aberration. So successful was this mirror that it still finds a fairly wide application for small lights. 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.

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