Excerpt from Photoelectric Spectrophotometry by the Null Method Another source of trouble in most deflection methods has been the difficulty of eliminating the so-called dark current; 1. E., the current through the cell when not irradiated.5 When this has not been completely eliminated or balanced, its magnitude has usually been measured and corrections made in the computa tions. Gradually, however, the technique of making photo electric cells has been improved, until now most of the cells made on the black-body -principle are found to obey very nearly the straight-line relationship, and the dark current can be much more easily suppressed. Nevertheless, a method which eliminates any. Possible errors and the necessity of any tests, calibrations, 'or corrections due to these two factors is of much greater value and reliability than is any method into which these factors may enter. 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.