Excerpt from Photo-Electricity
The first important observation on the action of light on the discharge of electricity from conductors was that of Hertz in 1887, who found that a spark passed between metallic terminals in air more easily when light from another spark fell on the negative terminal. This effect led to a number of investigations by Hallwachs, Elster and Geitel, and others, who found that electrified metallic conductors lost electrification when illuminated by a suitable source of light. On taking precautions to avoid spurious effects, the important result was established that the illuminated metal could lose negative, but not positive charges. If the metal were initially insulated and uncharged, then it acquired a small positive charge as a result of illumination, but the potential to which it rose did not exceed a volt. With most metals, the leak of negative electricity ceased on the interposition of a plate of glass between the source of light and the metal. As the glass absorbs the ultra-violet radiation, it was thus proved that the effect in these metals was due to ultra-violet light alone.
The alkali metals, on the other hand, were very sensitive to light of wave-lengths within the range of the visible spectrum as well as to ultra-violet light The leak of negative electricity from an illuminated plate occurred whether the metal was surrounded by a gas or was in the best vacuum obtainable, but the rate at which the leak took place varied considerably with the nature and pressure of the surrounding gas. Investigations were made by Stoletow and others soon after the discovery of the effect to determine the relations between the leak of electricity from the illuminated plate, and such factors as the pressure of the gas and the electric force outside the illuminated plate.
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. Это и многое другое вы найдете в книге Photo-Electricity (Classic Reprint)