Excerpt from The Illuminating Engineer, Vol. 13: Jan. 1920 to Dec. 1920 The circumstances in which apparatus for measuring illumination are applied and the number of purposes they serve are now so varied that there is room for quite a number of different forms. In each case a decision has to be taken as to the relative importance of accuracy and convenience. The tendency now is towards the design of very simple and portable instruments, in some cases allowing a reading to be taken by mere inspection of the scale without moving a lever to obtain balance. Such types form a valuable supplement to the more precise and accurate forms. One might suggest a rough classification into illumination-photometers and illumination-gauges, the latter serving merely to enable a rough determination of the order of illumination to be obtained with extreme ease and being suited to particular problems. For example, instruments for use in accurately determining conditions of illumination in streets, factories, picture theatres, mines, etc., demand qualifications that can only be met by a very comprehensive form of apparatus capable of adjustment according to the problem dealt with. 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.