April 17, 1914] 



SCIENCE 



559 



In fact, the term tendency is, in every 

 exact usage which you can give it, an es- 

 sentially statistical term. To say that a 

 has a tendency to lead to 6 is to declare 

 that a more or less certainly and definitely 

 known proportion of events of the class a 

 are followed by events of the class i. 



To introduce statistics into historical 

 study is simply to try to make some such 

 assertions about tendencies exact. 



The constant extension of the use of sta- 

 tistical methods in all the sciences of life 

 is something as familiar as it is momentous. 

 Its very familiarity, in fact, tends to blind 

 the minds of many to its real importance. 

 In truth, the statistical view of nature has 

 a logic of its own. Its three fundamental 

 conceptions, that of an average, that of ap- 

 proximation and that of probability, are in- 

 deed not the only fundamental categories of 

 our thought, but they are conceptions which 

 go down to the very roots of our own intelli- 

 gence as well as of our voluntary activity. 

 It seems increasingly plausible to assert that 

 these three conceptions, while they cer- 

 tainly have their special province, still, 

 within that province go down to the roots 

 of that nature of things which our sciences 

 are studying. At all events, I find it hard 

 to exaggerate the importance of those 

 methods and of those ideas of natural sci- 

 ence which are definable in terms of ap- 

 proximation and of probability, in the mod- 

 ern sense of those terms. 



When Clerk Maxwell made his threefold 

 classification of scientific methods, he did 

 so with his eyes well open to the fact that 

 by the statistical view of nature, and by 

 statistical methods in science he meant some- 

 thing much wider and deeper than is the 

 mere commonplace that statistical tables 

 can be made by the census bureaus, and can 

 be used by the insurance companies, or 

 applied to the discovering of various special 



laws of nature. Let me remind you of 

 what Maxwell had in mind. 



VII. THE STATISTICAL VIEW IN PHYSICS 



Clerk Maxwell was a physicist. His 

 greatest treatise was that upon electricity 

 and magnetism. The theory of electricity 

 and magnetism follows methods which il- 

 lustrate the mechanistic way of dealing 

 with the problems of nature. Maxwell de- 

 fined a system of differential equations in 

 terms of which certain elementary electro- 

 magnetic processes can be expressed. As- 

 suming these equations to be true, one can 

 compute the consequences of one's hypoth- 

 eses, as Newton computed the consequences 

 of supposing the law of the inverse 

 squares to be true for a field of gravitative 

 force. One can then compare the com- 

 puted results with experience, and upon 

 such computation and comparison with ex- 

 periment one's method in this case de- 

 pends. Such is an example of the essen- 

 tially mechanical view of nature. 



But Clerk Maxwell, working as he did at 

 a time when the general theory of energy 

 was in its period of most rapid develop- 

 ment, was not content to confine himself to 

 problems of the type of the theory of elec- 

 tricity. He also had his attention espe- 

 cially directed to those physical processes 

 which are illustrated by the diffusion of 

 gases, by the irreversible tendency of 

 energy to pass over from available to un- 

 available forms, and by various analogous 

 phenomena which can not be expressed in 

 terms of the classic types of mechanical 

 theories. 



Following the initiative of Clausius, but 

 developing along lines of his own, Maxwell 

 thereupon worked out his kinetic theory of 

 gases. It is that theory of which he is 

 thinking when he distinguishes the statis- 

 tical way of viewing nature both from the 

 historical and from the mechanical view. 



