Ebenezer Cunningham was a British mathematician and Cambridge graduate with an intense interest in the theory of special relativity, a subject that was just beginning to be recognised as he wrote. This book, first published by Cambridge University Press in 1914, was one of the first treatises in the English language to focus on special relativity. Its publication firmly established Cunningham as one of the greatest minds in the field. Within this volume, Cunningham firstly offers the reader a preface contextualising the progress of the study of relativity thus far. His chapters then process to relate relativity to existing physical theory, expanding on the relativity of Newtonian dynamics, electron theory and theories of Albert Einstein amongst others. This book is thoroughly and engagingly written, and promises to fascinate all those with an interest in the early study of special relativity.