Terrestrial Magnetism and Atmospheric Electricity, Vol. 22

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Excerpt from Terrestrial Magnetism and Atmospheric Electricity, Vol. 22: An International Quarterly Journal In many radioactive investigations in which the measurement of small currents is involved, the principle of allowing the current to enter an electrometer and escape through a standard high-resistance has been adopted, the deflection attained by the electrometer in the equilibrium state being the quantity which is directly measured, and which is proportional to the current sought, when the standard resistance obeys ohm's law. Bronson has developed a convenient type of resistance in which the air between two parallel plates is rendered conducting by covering one of the plates with a layer of polonium. These resistances obey ohm's law over a considerable range, but their magnitude is such that for plates of 5 or 6 sq. cm. cross-sectional area they give currents of the order of magnitude of 10¯² E. S. U. for potential-differences of 3 volts. For some purposes very much higher resistances are required, as for example when the current to be measured is very small and the conditions are nevertheless such that it is undesirable to make the electrometer very sensitive. The resistance may obviously be increased by increasing the distance between the plates or by reducing the intensity of the radioactive radiations, but such alterations are accompanied in general by a lowering of the potential range for which a linear relation between the current and the potential is obtained. 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.