ON THE STATISTICAL VIEW OF NATURE. 593 



undisputed and indisputable bases. 1 In proportion as 

 this has been done the calculated results have proved 

 to be in closer and closer accord with observed facts. I 

 will here mention only one of the latest achievements 

 in this line of research and reasoning. Assuming 

 as the atomic and kinetic theories do that all external 

 phenomena of bodies can be reduced to the collective 

 or mean effect of a practically infinite variety of tur- 

 bulent movements of a very large number of particles, it 

 must be possible to give a mechanical explanation of 

 that remarkable property of all phenomena of nature, 29. 



Irreversi- 



first noticed by Lord Kelvin, that they are essentially bmt 



> J natural 



irreversible i.e., that, with very rare exceptions, they P rocesses - 

 take place in a certain direction which we may define as 

 an equalisation of existing differences of level, tempera- 

 ture, electric pressure, and similar inequalities. In order 

 to fix this remarkable property of all natural phenomena, 

 physicists found themselves obliged to introduce, along- 

 side of energy and mass (which are both assumed to 

 conserve or maintain their total quantity), a third some- 

 thing which is the measure of the degree in which an 

 existing distribution of mass and energy can be con- 

 sidered to be capable of external, visible, finite activity 



1 Those who are interested in 

 seeing how difficult it is to link 

 together the common-sense argu- 

 ments of the theory of probabilities 

 in a consistent chain of unimpeach- 

 able logic, should read the report 

 on the various attempts to prove 

 Clerk-Maxwell's law (mentioned in 

 the foregoing note) contained in 

 Prof. 0. E. Meyer's ' Kinetische 

 Theorie der Case (2nd ed., Breslau, 

 1899), especially p. 46, &c., and 



VOL. H. 



' Mathematical Appendix,' p. 17 ; 

 and the great number of memoirs 

 referred to on p. 60 of that book. 

 Nevertheless Tait speaks of the still 

 remaining difficulties in the kinetic 

 theory of gases as having been 

 " greatly enhanced by an apparently 

 unwarranted application of the 

 theory of probabilities on which 

 the statistical method is based." 

 ('Properties of Matter,' 2nd ed., 

 1890, p. 291.) 



2 P 



