Norman Robert Campbell (1880-1949) was an English physicist and philosopher who made a significant contribution to the philosophy of science. In this book, which was first published in 1920, Campbell presents a detailed critical analysis of various areas of physics. Aimed at the advanced reader, with a 'familiarity with all the facts and theories of physics, ancient and modern', the text is divided into two main parts: the first part deals with 'The Propositions of Science' and the second discusses aspects of 'Measurement'. An appendix and detailed index are also included. This book will be of value to anyone with an interest in the development of physics and the history of science.