36 Mr. F. Galton on Statistics by Inter comparison , 



tude of the object that stands at a distance x from that end of 

 the base where the ordinates are smallest, then the number of 





Fig. 



1. 



















objects less than y : the number of objects greater thany : : x : n— x. 

 The ordinate m at \ represents the mean value of the series, and 

 Pj q at 5 and f , taken in connexion with m, give data for estima- 

 ting the divergence; thus q—m is the divergence (probable 

 error) of at least that portion of the series that is in excess of 

 the mean, andm— p is that of at least the other portion. When 

 the series is symmetrical, q — m—p—q, and either, or the mean 

 of both, may be taken as the divergence of the series generally. 

 No doubt we are liable to deal with cases in which there may 

 be some interruption in the steady sweep of the ogive; but 

 the experience of qualities which we can measure, assures us 

 that we need fear no large irregularity of that kind when dealing 

 with those which, as yet, we have no certain means of measuring. 

 When we marshal a series, we may arrange them roughly, 

 except in the neighbourhood of the critical points ; and thus 

 much labour will be saved. But the most practical way of 

 setting to work would probably depend not on the mere dis- 

 crimination of greater and less, but also on a rough sense of 

 what is much greater or much less. We have called the objects 

 at the J, \ y and £ distances p, m, and q respectively ; let us sort 

 the objects into two equal portions P and Q, of small and great, 

 taking no more pains about the sorting than will ensure that P 

 contains p and all smaller than p, and that Q contains q and all 

 larger than q. Next, beginning, say, with group P, sort away 

 alternately to right and left the larger and the smaller objects, 



