Excerpt from Proceedings of the American Academy of Arts and Sciences, Vol. 57: From May 1921, to May 1922 Therefore which pole is soaked makes no difference, nor does it matter which pole is above. The region near the pole generally shows the grid in the echelon, that near the pole a broad structure less line. The grating always gives a narrow unreversed line or one very slightly reversed where the echelon shows the grid, and a strongly reversed line where the echelon shows no structure. Thus the grid does not result from conditions which produce a reversed grating line. With Li a67o8, which usually appears widely reversed in the grat ing, the grid is more difficult to Obtain in the echelon, while with Na A4972 given as an unreversed line by the grating at either edge or centre of the arc image the echelon shows the grid at both edge and centre. 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.