224 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 



and how similar changes are beginning to occur in the attitude of 

 the chemists. The importance of Einstein's work thus lies not so 

 much in the facts or phenomena that can be explained by the rela- 

 tivity theory, but in the discovery of a new way of thinking as 

 applied to physics. Somewhat similar methods of thought had, it 

 is true, been used in some branches of mathematics and sometimes 

 in philosophy, but Einstein subjected our elementary conceptions of 

 space, time, mass, energy, etc., to a searching analysis quite new in 

 the history of physics. 



CONCEPTS INVOLVE OPERATIONS 



Prof. p. W. Bridgman, of Harvard University, has recently written 

 a popular book entitled "The Logic of Modern Physics," in which he 

 analyzes the changes in our concepts that have resulted primarily 

 from Einstein's work. Bridgman's thesis is that physical concepts 

 have meaning only in so far as they can be defined in terms of opera- 

 tions. He shows that this new attitude toward our fundamental con- 

 ceptions is perhaps one of the greatest changes that has been brought 

 about by Einstein's work. There is no question in my mind but that 

 the recent remarkable advances in quantum mechanics that have been 

 made by such men as Bohr, Heisenberg, Schroedinger and Dirac have 

 been stimulated by the desire to formulate all concepts in terms of 

 operations. Bridgman has not originated this method, but he, more 

 than anyone else, perhaps, has been conscious of its widespread appli- 

 cation in modern physics. 



I should like to outline to you the way in which Bridgman de- 

 velops this thesis and to consider how well it applies to the most 

 recent changes that have taken place in physics and in chemistry. I 

 believe the chemist can derive great benefit from the conscious appli- 

 cation of a similar critical attitude in his own science. 



Bridgman points out that " hitherto many of the concepts of 

 physics have been defined in terms of their properties." An excellent 

 example is Newton's concept of absolute time. The following quota- 

 tion from Newton's Principia is illuminating. 



I do not define Time, Space, Place, or Motion, as being well known to all. 

 Only I must observe that the vulgar conceive those quantities under no other 

 notions but from the relation they bear to sensible objects. And thence arise 

 certain prejudices, for the removing of which, it will be convenient to distin- 

 guish them into Absolute and Relative, True and Apparent, Mathematical and 

 Common. 



(1) Absolute, True and Mathematical Time, of itself, and from its own nature 

 flows equally without regard to anything external, and by another name is 

 called Duration. 



Thus, according to Newton, time and space have properties of a 

 very abstract kind and are looked upon as "things" which exist inde- 



