Published in 1970: The leading idea of the book is that present knowledge only enables us to maintain our present state, that national progress is the result of new ideas, and that the chief source of new ideas is original research. That as advance has its origin in new knowledge; unless new discoveries are made, new inventions and improvements must sooner or later cease. Another prominent idea is, that truth is essentially the same in all divisions of knowledge, and that the mental powers and processes employed in detecting it are the same in all subjects.