260 THE HISTORY OF SCIENCE 



mine with precision the conditions of their existence 

 and succession. Thus science after contemplating a 

 wide range of outer phenomena plants, animals, 

 earth's crust, heavenly bodies, molecules and atoms 

 turns its attention with keen scrutiny inward on 

 the thinking mind, the subjective process by which 

 man becomes cognizant of all objective things. 



The need of expert study of the human mind as 

 the instrument of scientific discovery might have been 

 inferred from the fact that the physicist Tyndall read 

 before the British Association in 1870 a paper on the 

 Scientific Use of the Imagination, in which he spoke 

 of the imagination as the architect of physical theory, 

 cited Newton, Dalton, Davy, and Faraday as afford- 

 ing examples of the just use of this creative power 

 of the mind, and quoted a distinguished chemist as 

 identifying the mental process of scientific discov- 

 ery with that of artistic production. Tyndall even 

 chased the psychologists in their own field and stated 

 that it was only by the exercise of the imagination that 

 we could ascribe the possession of mental powers to 

 our fellow creatures. " You believe that in society 

 you are surrounded by reasonable beings like your- 

 self. . . . What is your warrant for this conviction ? 

 Simply and solely this : your fellow-creatures behave 

 as if they were reasonable." 



On the traces of this brilliant incursion of the 

 natural philosopher into the realm of mental science, 

 later psychologists must follow but haltingly. Just 

 as in the history of physics a long series of studies 

 intervened between Bacon's hypothesis that heat is 

 a kind of motion (1620) and Tyndall's own work, 

 Heat as a Mode of Motion (1863), so must many 



