DISCOVERT BY MEANS OF INFERENCE. 585 



before we evolve new discoveries from them by means of 

 inference. 



All the great modern theories of science have been 

 discovered by the employment of inference. It was by 

 means of that method that the theories and principles of 

 universal gravitation, of the universality of matter and of the 

 physical powers, of the conservation of matter and energy, 

 of the transmutation and equivalence of forces, &c. &c., 

 have been evolved. It was by inference from a great 

 many facts that Sir Isaac Newton, and others who suc- 

 ceeded him, established the principle of gravitation, and 

 proved its existence and operation in distant parts of the 

 universe. By the same method, Faraday and others 

 established the universality of magnetism ; and by in- 

 ference from the results of numerous investigators the 

 comprehensive truth has been discovered, that all the 

 forces upon this earth are modes of one primary energy. 

 It has been by means of inference from the results of the 

 labours of numerous eminent chemists that we acquired 

 the great truth that we never create or destroy matter ; 

 and from the results obtained by Joule and others, respect- 

 ing the conversion of one mode of energy into another, 

 and the quantitative relations of the various physical 

 powers, we discovered the great truth that we are also 

 unable to create or destroy energy. But whilst inference 

 is the most powerful intellectual method we yet possess 

 for discovering important and abstruse truths, it is, at the 

 same time} the one which requires the greatest degree of 

 preparation of the senses and mental powers. No man 

 can infer unless he can compare ; nor compare unless he 

 can perceive. Ability in comparing is based upon the 

 possession of extensive knowledge, by observation or other- 

 wise ; and that of inferring is founded upon comparison, 

 and ready detection of real similarity or difference. 



