Excerpt from Instruction in Army Telegraphy and Telephony, Vol. 1: InstrumentsIn (a) and (6) chemical energy is converted into electrical energy, and in (c) mechanical energy is converted to electrical energy.For telegraph work and the speaking portions of telephones, primary batteries are generally used, and in the field they are always used.Secondary batteries (accumulators) are used in large civil telegraph offices and telephone exchanges.About the PublisherForgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.comThis 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.