108 



THE WORLD OF LIFE 



CHAP. 



thousands the curves would be equally regular ; and this 

 has now been found to be the case. 



The law alluded to is that the number of individuals 

 showing any particular amount of variation is in inverse 

 proportion to its departure from the mean value in the 

 species. It is very closely represented by a special curve 

 called by mathematicians the " curve of error," but for our 

 purpose may be termed the curve of frequency. 



The diagram here given represents this curve obtained 



Dwarfs. Average Men Giants. 



CURVE OF STATURE. (BRITISH). 



FIG. 9. DIAGRAM OF HEIGHT OF 2600 MEN. 



by measuring the heights of a large number of men taken 

 at random. 



The horizontal scale shows the heights given in feet and 

 inches, and the vertical scale the numbers measured of succes- 

 sive heights. The central line through the highest point of 

 the curve marks the average of the whole number measured, 

 there being in this case (though not always) very nearly the 

 same number of individuals above and below the mean 

 height. 



The peculiarity of the curve is that it rises very slowly 

 from the height marking that of the shortest individual 

 measured here a fraction above 4 feet 8 inches then 

 more and more rapidly for about one-third of the height, 

 then more rapidly and nearly regularly to near the summit, 

 when it bends in rather abruptly to the mean height, and 

 then descends in a nearly corresponding curve as heights 

 are above the average, till it ends just short of 6 feet 

 8 inches. 



