602 



SCIENTIFIC THOQGHT. 



The conceptions involved in the atomic and kinetic 

 views of natural processes, and the statistical manner of 

 dealing with these crowds of moving particles, have thus 

 introduced into natural philosophy two distinct and novel 

 considerations not known to former ages : first, the con- 

 sideration that our knowledge of things and phenomena 

 in nature is not historical, but that it is that of the 

 mean or average and of the total effects produced by an 

 immensely large number of singly imperceptible events 

 upon our senses which are too coarse to receive or deal 

 with individual occurrences ; secondly, the consideration 

 that our knowledge is not purely mechanical, inasmuch 



history of each separately, so that, 

 in order to reduce their labour 

 within human limits, they concen- 

 trate their attention on a small 

 number of artificial groups. The 

 varying number of individuals in 

 each group, and not the varying 

 state of each individual, is the 

 primary datum from which they 

 work. This, of course, is not the 

 only method of studying human 

 nature. We may observe the eon- 

 duct of individual men and compare 

 it with that conduct which their 

 previous character and their present 

 circumstances, according to the best 

 existing theory, would lead us to 

 expect. Those who practise this 

 method endeavour to improve their 

 knowledge of the elements of 

 human nature in much the same 

 way as an astronomer corrects the 

 elements of a planet by comparing 

 its actual position with that de- 

 duced from the received elements. 

 The study of human nature by 

 parents and schoolmasters, by his- 

 torians and statesmen, is, there- 

 fore, to be distinguished from that 

 carried on by registrars and tabu- 

 lators, and by those statesmen who 

 put their faith in figures. The one 



may be called the historical and 

 the other the statistical method. 

 The equations of dj-namics com- 

 pletely express the laws of the 

 historical method as applied to 

 matter, but the application of these 

 equations implies a perfect know- 

 ledge of all the data. But the 

 smallest portion of matter which 

 we can subject to experiment con- 

 sists of millions of molecules, not 

 one of which ever becomes sensible 

 to us. We cannot, therefore, ascer- 

 tain the actual motion of any one 

 of these molecules ; so that we are 

 obliged to abandon the strict his- 

 torical method of dealing with large 

 groups of molecules. The data of 

 the statistical method, as applied to 

 molecular science, are the sums of 

 large numbers of molecular quan- 

 tities. In studying the relations 

 between quantities of this kind, we 

 meet with a new kind of regularity, 

 the regularity of averages, which 

 we can depend upon quite suffi- 

 ciently for all practical purposes, 

 but which can make no claim to 

 that character of absolute precision 

 which belongs to the laws of 

 abstract dynamics." 



