28 Arrangement and Formation of the Series. [CHAP. n. 



numerous than his bad ones. Here again, then, we have 

 a series of magnitudes (i.e. the deflections of the shots from 

 the point aimed at) clustering about a mean, but produced 

 in a very different way from those of the last two cases. 

 In this instance the elements would be commonly regarded 

 as only partially the results of human volition, and chance 

 therefore as being only a co-agent in the effects produced. 

 With these must be classed what may be called estimates, 

 as distinguished from measurements. By the latter are 

 generally understood the results of a certain amount of 

 mechanism or manipulation; by the former we may under 

 stand those cases in which the magnitude in question is 

 determined by direct observation or introspection. The 

 interest and importance of this class, so far as scientific 

 principles are concerned, dates mainly from the investigations 

 of Fechner. Its chief field is naturally to be found amongst 

 psychological data. 



Other classes of things, besides those alluded to above, 

 might readily be given. These however are the classes about 

 which the most extensive statistics are obtainable, or to 

 which the most practical importance and interest are at 

 tached. The profound distinctions which separate their 

 origin and character are obvious. If they all really did 

 display precisely the same law of variation it would be a 

 most remarkable fact, pointing doubtless to some deep- 

 seated identity underlying the various ways, apparently 

 so widely distinct, in which they had been brought about. 

 The questions now to be discussed are; Is it the case, 

 with any considerable degree of rigour, that only one law 

 of distribution does really prevail ? and, in so far as this 

 is so, how does it come to pass ? 



of shots which strike the bull s-eye so much less surface than any of the 

 will not be the greatest, since it covers other circles. 



