202 



THE RATE OF GROWTH 



[CH. 



dimensions is nearly over*. The ratio W/H^ increases steadily, 

 and at three years old is double what it was at birth. It is the 

 most variable of the' three ratios; and it so illustrates the some- 

 what obvious but not unimportant fact that k varies most for the 

 dimension which varies least, or grows most uniformly; in other 

 words, that the values of k, as determined at successive epochs for 

 any one dimension, are a measure of the variability of the other two. 

 The same ponderal index serves as an index of "build," or 

 bodily proportion; and its mean values have been determined for 

 various ages and f6r many races of mankind. Within one and the 





60 



70 



65 



Height (inches) 



Fig. 53. Ratio of height to weight in man. From Goringe's data. 



same race it varies with stature ; for tall men, and boys too, are apt 

 to be slender and lean, and short ones to be thickset and strong. 

 And so much does the weight-length ratio change with build or 

 stature that, in the following table of mean heights and weights of 

 men between five and six feet high, it will be seen that weight, 

 instead of varying as the cube of the height, is (within the hmits 

 shewn) in nearly simple linear relation to it (Fig. 53) f. 



* As a matter of fact, the data shew that the animal grows under 7 per cent, 

 in length, but over 11 per cent, in height, between the twentieth and the thirtieth 

 month of its age. 



t Had the weights varied as the cube of the height, the tallest men should 

 have weighed close on 200 lb., instead of 160 lb. 



