408 MR. K. PEARSON ON THE MATHEMATICAL THEORY OF EVOLUTION. 
(B.) Mortality of Middle Life. 
Total frequency = 173°2. 
Centroid-vertical at 41°5 years. 
Maximum mortality = 5:4. 
The curve is very approximately normal, and has a standard deviation of 12°8 
years. The corresponding French component = 180 deaths, standard deviation 
12 years, with a maximum of 6 at 45 years. 
(C.) Mortality of Youth. 
Total frequency = 50°8. 
Centroid-vertical at 22°5 years. 
Maximum mortality = 2°6. 
The curve is very approximately normal, with a standard deviation of 7°8 years.* 
The corresponding French component gives a total mortality of 78, standard deviation 
of 6 years, and a maximum of 5'2 at 22°5 years. 
The greater and more concentrated French mortality of youth is noteworthy. 
(D.) Mortality of Childhood. 
Total frequency = 46°4. 
Centroid-vertical at 6°06 years, 
Maximum mortality = 9 at 3 years. 
The equation to the curve, the axis of y being maximum ordinate, is 
y = 9 (1 + ai) e@7 eet. 
Thus the skewness of the curve = ‘87, and the range commences at 2 years. 
The French component appears to be shifted further towards youth. It gives a 
total of 47 deaths, centroid at 8°75 years, and a maximum of 5°8 at 5°75 years, 
skewness = ‘71. Childish mortality is therefore, if these results be correct, more 
concentrated, and at an earlier age in England than in France. 
(E.) Infantile Mortality. 
Total frequency after birth = 245-7. 
Maximum frequency after birth occurs in first year and equals 156:2. 
The equation to the frequency curve is 
y = 236°8 (w + °75)-* e-™, 
the origin being at birth, the skewness °707, and the centroid at ‘083 year,= 1 month 
neatly, before. birth. Taking the corresponding French component, we have a total 
frequency after birth of 284, with 186 deaths in the first year of life. Infantile 
mortality is therefore considerably greater in France. 
* The mortality of youth would be better expressed by a curve of type y= Yo (i — 
§ 13 (v.). 
ge \m 
: see our 
2 
ar 

