Excerpt from Journal of the Institution of Electrical Engineers, Vol. 37: Including Original Communications on Telegraphy and Electrical Science Whilst it is the usual and, for some purposes, more useful practice to Specify the efficiency of an arc lamp in candle power per watt, it is thought that the candle power per ampere may also be a useful figure. It will be remembered that in the discussion that took place a few years ago on the question of changing the pressure of supply from 100 to 200 volts, a favourite argument used by those opposed to the change was that the majority of tradesmen using arc lamps required two lamps only, and that, should the pressure be doubled, these consumers would be forced either to alter their wiring and install four lamps where they only required two, or to absorb over 50 per cent. Of the total energy in useless resistance. T he introduction of the high-voltage enclosed arc lamp, however, overcame this difficulty, and in spite of its low efficiency per watt its use has now become very general. In considering improvements in arc lamps it is necessary, therefore, to bear in mind that, for many purposes, low-voltage lamps cannot be used to the greatest advantage. Returning to the question of long arcs versus short arcs, it is an interesting fact that all the very marked improvements that have been made in arc lighting during recent years have been effected by the use of arcs of from IO to 15 millimetres in length, and investigation shows that the great improvement in efficiency is directly or indirectly due to this increased length. 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.