Ernest William Brown (1866-1938) was a prominent British mathematician and astronomer renowned for his contribution to the study of lunar motion. Originally published in 1932, this concise volume was based on a series of lectures given at the Rice Institute during April 1931. It consists of an attempt to describe and analyse the phenomena which are peculiar to resonance in an elementary manner. Although of fundamental importance to many mechanical problems, this subject had received comparatively little attention in textbooks at the time of publication. Treatment consists of an investigation of the changes which take place in the amplitude and phase of a vibrating element under certain types of forces. This book will be of value to anyone with an interest in Brown's writings and the theorization of resonance.