Excerpt from Displacement Interferometry by the Aid of the Achromatic Fringes The following account of my experiments has been given chronologically. Although many of the anomalous features, in which the interferences of superposed coordinated spectra first presented themselves, were largely removed in the later work, yet the methods used in the several papers, early and later, are throughout different. It therefore seemed justifiable to record them, together with the inferences they at first suggested. The pursuit of the subject as a whole was made both easier and more difficult by the unavoidable tremors of the laboratory in which I am working; for it is possibly easier to detect an elusive phenomenon if it is in motion among other similar stationary phenomena. But it is certainly difficult, thereafter, to describe it when found. It will be convenient to refer to the cases in which one of the two coincident spectra from the same source is rotated 180 with reference to the other on a transverse axis (i. e., an axis parallel to the Fraunhofer lines), under the term reversed spectra; while the term inverted spectra is at hand for those cases in which one of the paired spectra is turned 180 relative to the other on a longitudinal axis (i. e., an axis parallel to the r-v length of the spectrum). In this book the latter are merely touched upon, briefly, in Chapter I, but they are now being investigated in detail and give promise of many interesting results. The chapter contains a full account of what may be seen with a single grating - the linear phenomenon, as I have called it, and which, if it stood alone, would be difficult to interpret. In Chapter II, therefore, the interferences of reversed spectra are treated by the aid of two gratings, in virtue of which a multitude of variations are inevitably introduced. The phenomena are thus exhibited in a way leading much more smoothly to their identification. This endeavor is given greater promise in Chapter III, which contains a comparison of the interferences of reversed and non-reversed spectra, the latter produced in a way quite different from those in my earlier work. Naturally these in their entirety are even more bewilderingly varied, and become particularly so when, as in Chapter IV, an intermediate reflection of one spectrum is admitted. But with this I was on more familiar ground, as I have hitherto, in these publications, given such investigations particular attention. The flexibility of the new methods is well shown in Chapter V, where separated component beams can with equal facility be made to run in parallel, or across each other at any angle, and perhaps both, with the double result visible in the field of the telescope. In case of crossed rays a remarkable phenomenon is shown, in which very small differences in wave-length imply a remarkably large difference in rotational phase (virtually resolving power) of the two interesting groups of interference fringes due to each wave-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."