midable the chances of such visitations being lessened, on the other hand, by agricultural improvements and by varying the means of subsistence. Medical Skill and Public Hygiene have equally discovered valuable means of combating mortality, whilst the development of industrial pursuits, and the guarantees afforded to society by more liberal institutions, have lent their aid to diffuse prosperity, and the most active means of preservation." The RegistrarGeneral of England says:-"Without affirming, on physiological grounds, that man was created to live a destined number of years, or to go through a series of changes which are only completed in 80, 90, or 100 years, experience furnishes us with a standard which can only be said to be too high. 17 in 1,000 is supplied as a standard by experience. Here we stand upon the actual. Any deaths in a people exceeding 17 in 1,000 annually are unnatural deaths. If the people were shot, drowned, burnt, poisoned by strychnine, their deaths would not be more unnatural than the deaths wrought clandestinely by disease, in excess of the quota of natural deaths; that is, in excess of seventeen deaths in 1,000 living."

As an instance of the saving of life which has been caused by the progress of civilisation and of hygiene, we may mention London, the annual mortality of which two centuries ago was 50 per 1,000, its inhabitants living only 20 years on an average. The yearly death-rate was:-1660-79, 80.0; 1681-90, 42.1; 1746-55, 35·5; 1846-55, 24.9; 1871, 22.6. The annual death-rate is now only 24 per 1,000, and the mean duration of life 42 years. Even within the past few years a great decline has taken place in the death-rate of many places in England which have had the benefit of sanitary improvements. Dr. Buchanan embodies the facts in a Table, an abstract of which is appended.

1 Report for Quarter ended December, 1857.

118

CHAPTER VIII.

POPULATION.

Definition of Population.-Specific Population-Absolute Population.—Increase of Population dependent on Excess of Births over Deaths, and on Immigration.-Law of increase of Population.-Checks to its Increase.-Formula.-Density of Population.-Effective Population.-"Stationary" Population.-Census of United Kingdom in 1871.— Results relating to England and Wales, Scotland, and Ireland.

In the preceding chapters we have considered the statistical inquiries connected with the birth and death of man. It now becomes necessary to investigate the bearing of these inquiries on the body politic of mankind-in other words, to consider the laws of population.

The population, or the number of inhabitants of a country, district, or town, may be expressed in two ways: first, as the numerical total of the individuals; secondly, as the number of inhabitants to each unit of area, such as an acre, a square mile, etc. The latter is the specific population (Quetelet), a far more important datum in questions of political economy or of hygiene than the mere absolute population. With regard to political economy, Quetelet remarks that if all physical conditions were the same in the different countries of Europe, there would be no better gauge of the productive and industrial powers of a country than the density of its population. With regard to hygiene, it will be shown in a subsequent chapter how intimate are the relations between public health and density of population.

Increase of population depends on an excess of births over deaths, and on immigration. It is more or less rapid according to the prosperity of, and the facility of obtaining the means of subsistence amongst, a community. Towards

the close of the last century Malthus laid down the proposition that population, when unchecked, goes on doubling itself every 25 years, or tends to increase in a geometrical ratio—that is to say, the human race may, under the most favourable circumstances, increase in a ratio corresponding to the series of numbers 1, 2, 4, 8, 16, 32, 64, etc. The truth of this proposition is accepted by the foremost statisticians of later years. Malthus also arrived at the conclusion that the increase of food, depending on the fertility of land, its reclamation, and improvements in agriculture, advanced only in an arithmetical progression, or in a ratio corresponding to the series of numbers 1, 2, 3, 4, 5, 6, etc. This proposition has proved to be as well founded as the former. But Malthus, in venturing to theorise on the appalling results which would follow the action of these laws, overlooked the element of free trade, which enabled a nation to draw upon the fertility of the world at large for the sustenance of its own increasing population. In consequence of this, the true philanthropy of the man was lost sight of, and he was most undeservedly looked upon as the enemy of the poorer classes.

The checks to the increase of any population may be ranged under two heads-preventive (l'obstacle privitif—Quetelet) and positive ((l'obstacle destructif-Quetelet). When an increasing population has reached the limit of its means of subsistence, the former check should come into play through the reason and foresight of the individual members of the population. This moral restraint is the prudential withholding from marriage, with a conduct strictly moral during the continuance of the restraint. It may be practised for a limited period or throughout life. The positive check to increase of population is expressed by the words vice and misery. A writer in the Penny Cyclopædia1 well sums up factors included under these terms:- Vice, promiscuous sexual intercourse, unnatural passions, violation of the

1 Article: Population. Vol. xviii. P. 408.

the

Kei Emer arts to conceal the consequences of Sonnexions; Misery, unwholesome occupations, kee“, exposure to the seasons, extreme poverty, bad Na Gldren, excesses of all kinds, the whole train of JALAN JERES and epidemics, wars, plagues, and famines. se the operation of all these checks in a varying the population of a country is seldom seen increasing 3 x metrical progression. The United States show an ze of population from 1780 to 1825 which is only in smoosi progression. This is exhibited in a table given Juozolor

In this case the annual increase may be regarded as 190,822. Representing this difference by d, the population in 1780 by P, and a number of years by z, the population of the year is found by the equation:—

Px=P+ dx.

This formula may be employed for estimating the rate of increase of population in any place or country. But it must be remembered that the annual increase of population of a country is an inaccurate basis on which to ground a calcucation as to the period within which that population will double itself.

** using example of the fallacies likely to arise from adopting, for