Segar. — The Population of Neio Zealand. 447 



If a population had such a distribution, and if the annual 

 number of births and the rates of mortality at the several 

 ages were to remain constant, the population would be 

 stationary — that is, would itself also remain constant in re- 

 spect both to total and to age distribution ; for the popula- 

 tion at any age would be replaced, after any number of years, 

 by an equal population of the same age. For such a popula- 

 tion the birth-rate would be constant ; and, further, the total 

 population being constant, the annual number of deaths 

 would be equal to that of births, and the death-rate would 

 consequently be constant and equal to the birth-rate. What 

 this common birth- and death-rate would be for any country 

 would depend on the rates of mortality of the people ; the 

 more favourable the rates of mortality the greater would be 

 the total population due to a given annual number of births, 

 and hence the smaller would be the birth- and death-rate. 

 For each country we should have a different stationary distri- 

 bution, varying according to the rates of mortality at the 

 several ages obtaining. 



Any increase or decrease in the magnitude of a population 

 having a stationary distribution could take place only through 

 an increase or decrease in the annual number of births or by 

 changes in the rates of mortality. 



A portion only of a population contained between any two 

 ages may have a stationary distribution independently of the 

 rest of the population. In such a case, if the rates of mortality 

 remain constant, an increase or decrease of its total can follow 

 only from a corresponding change in the numbers entering in 

 the course of time from the ranks of those of inferior ages or 

 from excess of immigration or emigration. 



If the annual number of births be constant for any number 

 of years in any country whose population is not materially 

 disturbed by immigration and emigration, a stationary distri- 

 bution of ages is produced throughout that portion of the 

 population born within the period. Thus almost the whole 

 population of France has a practically stationary distribution 

 of ages, with the result that the population as a whole is 

 almost stationary ; while at the last census the distribution 

 of the population of New Zealand was stationary for the ages 

 0-17, as a result of a practically constant annual number of 

 births having obtained in the colony for about a correspond- 

 ing number of years. 



The following table gives the age-distributions of the popu- 

 lation of New Zealand for the years 1881 and 1896, and that 

 corresponding to a stationary state, on the basis of an annual 

 number of births of 20,000. The rates of mortality made use 

 of here and elsewhere are those published for New Zealand by 

 Mr. C. E. Adams, B.Sc, A.I. A., F.S.S., in the "Transactions 



