110 



THE WOKLD OF LIFE 



fore giving examples of the variation of the higher animals 

 it will be advisable to show Avhat is meant bv the " law of 

 frequency " of variations which has been established by the 

 measurement of several thousands of men in various countries 

 of Europe. These when recorded by means of a diagram are 

 found to form a very regular curve, which becomes more and 

 more regular the larger are the numbers measured. The im- 

 portance of this is that when we have only small numbers of 

 animals to deal with, and we find great irregularity in their 

 diagrams, we are sure that if we had measurements of hun- 

 dreds or 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 show- 

 ing 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 eiTor," but for our purpose may be termed the 

 curve of frequency. 



The diagram here given represents this curve obtained by^ 



mimm 



^i^V:::^::::::.::..:... 



Dwarfs. Average Men Giant*. 



CURVE OF STATURE. (BRITISH). 



Fig. 9.— Diagi-am of Heiglit of 2600 Men. 



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 suc- 

 cessive heights. The central line through the highest point of 



