Excerpt from An Introduction to the Study of Variable Stars During the past few years the subject of variable stars has become increasingly interesting to the amateur who is the owner of a telescope, as well as to the average college student who has some knowledge of astronomy, while to the research worker it offers many line of investigation which are full of promise. However, so complex is the subject, and so diverse the principles involved in a complete understanding of it, that extensive reading in several different directions is required as a foundation. It is with the purpose of supplying this need as well as of making an important and attractive branch of astronomy accessible to the student that the present volume has been prepared. It is the outcome of several years of teaching the subject in Vassar College, for which the material was primarily collected. This material is scattered throughout various periodicals in the form either of research papers or quite popular articles, intended to give directions for observation to owners of small telescopes. A large amount of historical matter is also included, which is taken from sources not within easy reach of the general reader. Mention may be made of some of the subjects treated, which are introductory to the study of stellar variation, such as the study of the Durchmusterung charts, photometry in all its branches, spectroscopy, and star color. The purpose of the present volume is to consider all of these points, and in particular to give in as simple and clear a form as possible a full presentation of the physical principles upon which many of the instruments and methods of investigation are based, principles such as those of polarized light, spectrum analysis, the formation of the photographic image, and photo-electricity. 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.