Lanterna Rally

Author: Burton McCollum

Publisher: Forgotten Books

Published: 2016-09-28

Total Pages: 34

ISBN-13: 9781333782078

Excerpt from A New Method for the Absolute Measurement of Electric Quantity Although the current balance is capable of yielding a high degree of accuracy, it is not desirable to depend on the value given by a single type of apparatus, even though the experiments may be repeated with good agreement by different experimenters and with different instruments. It is highly desirable that if possible the values be checked by some other method, using a totally different type of apparatus. In electrodynamometers of the ordinary types the dimensions of the windings must be known with extreme accuracy, thus requiring that the coils not only be wound with great regularity and measured with great care, but permanency of both size and form must be assured. In the Gray electrodynamometer a greater difficulty still is met with in measuring the torque. This is accomplished by balancing the torque due to the current against the torsion of a wire, the constant of which has been determined by a separate experiment. The great difficulty in this lies in the erratic behavior of all materials available for the torsion wire. They can not be depended upon to remain constant with time, they vary considerably even with slight changes in temperature, and they all have a greater or less tendency to take a permanent set when twisted, as they must be, in use. Again, both electro dynamometers and current balances have a rather troublesome temperature coefficient, and, although artificial cooling may alleviate this condition somewhat, a certain amount of local heating is inevitable, and the consequent change in the dimensions may give rise to considerable variation in the constants of the instruments between the time of measuring the dimensions of the coils and the time of making a measurement of current. In what follows, there is described a type of electrodynamometer which, when used to measure the electrochemical equivalent of silver, appears to be free from the objections referred to above, and at the same time it is believed that no other difficulties of a serious nature are introduced. 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.