Excerpt from Journal of Experimental Psychology, 1917, Vol. 2<br><br>F rom this point of View they are (i) the total radiant power density, or the number of ergs of radiant energy of all wave-lengths, striking the retina, per unit area, per unit time. This is the integral of the energy distribution curve for unit time and area, and is what would be measured by a surface thermopile (at the retina).<br><br>About the Publisher<br><br>Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com<br><br>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.