Excerpt from A Dictionary of Electrical Words, Terms and Phrases, Vol. 2: T to Z Since, when either key is moving there is a small interval of time when the circuit is broken for incoming currents, the keys are generally made so as to close the second contact before breaking the first. In order to avoid disturbing the balance on the introduction of the resistance of the batteries at A or B, on closing the circuits, an equal resistance is added at r and r', between the back stop and the earth. Since the proper Operation of duplex telegraphy requires a balance in the resistance of the circuits of the differentially wound coils, a rheostat at R, and R', is necessary. Besides balancing the line for resistance, it is necessary to balance it for capacity. A condenser is, therefore, necessary when the circuit exceeds in length about too miles, or has much cable or underground wire. Telegraphy, fac-simile - A system whereby a fac-simile or copy of a chart. Diagram, picture or signature is telegraphically transmitted from one station to another. Facsimile telegraphy is sometimes called auto. Graphic telegraphy, or pantelegraphy. 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.