6 Mr. T. R. Edmonds on the Law of Human Mortality 



observations made on the population of England, the point of 



junction of the two periods is very near the age 9 years and 4 



months from birth-time. But in seven out of eight of the 



Tables of comparison hereunto annexed, the column which 



exhibits the results of the new formula is taken from a Table in 



which the period of childhood is assumed to terminate at the 



age of 9 complete years, and the period of manhood to commence 



at 12 years of age. The rate of mortality or rate of decrement 



of life, in the intermediate period from 9 to 12 years of age, has 



been assumed to be constant and at a minimum of *0055 per 



•0055 . . ,, 

 annum, or m time at. 



9 

 The two branches of the curve indicating the law of decrease 



of human life (before 9 and after 12 years of age) bear a simple 

 relation to one another. If the abscissae of the two curves, 

 between the zeros of life and the ages of minimum mortality, 

 be divided into the same number of equal parts, the logarithms 

 of the corresponding ordinates are to one another in a fixed pro- 

 portion, that of 1 to 8 very nearly. If the period of childhood, 

 extending from — 2^ years to +9 years of age, be divided into 

 15 equal parts of 9 months each, and the period of manhood, 

 extending from 12 to 102 years of age, be divided into the same 

 number of equal parts, each of 6 years, in that case the rate of 

 mortality will decrease in any one of the 15 equal intervals into 

 which the period of childhood is divided, exactly eight times as 

 fast as the rate of mortality in the corresponding interval of 

 manhood increases. The vital force being inversely as the rate 

 of mortality, it ensues that the increase of vital force in passing 

 through any interval of 9 months in the period of childhood is 

 exactly counterbalanced by a decrease of vital force in passing 

 through the corresponding interval of 6 years in the period of 

 manhood. The existence of the relations now mentioned 

 between the two branches of the curve of life, renders it unne- 

 cessary to make separate calculations by the new formula for 

 the values of logP in both curves; for when logP is known 

 for one curve, it is known for the other curve also, by the use 

 of a constant multiplier, as may be seen on reference to Table III. 

 hereunto annexed. On reference to Table II. hereunto annexed, 

 it will also be seen, at each of 15 intervals of age, how nearly 

 the rates of decrement in the period of childhood resemble those 

 of corresponding ages in the period of manhood, according to 

 the English Life Table No. 3 for males. 



The only good observations in the rates of decrement, accord- 

 ing to age, prevailing in the general population of a nation are 

 those which have been made in Sweden and in England. The 

 Swedish observations commence with the year 1 749 ; the English 



