Originally published in 1911, this book was based upon a series of four lectures delivered at the University of Calcutta during March 1908 by the renowned German-born British physicist Arthur Schuster (1851-1934). The text provides a concise discussion of advances in physics during the period 1875-1908 and Schuster's position in relation to contemporary theories, including those of Einstein and Planck. This book will be of value to anyone with an interest in the development of physics and the history of science.