It has been usual to consider a great proportion of births as the surest sign of a vigorous and flourishing state. But this is erroneous. Only after great mortality, or under very especial social conditions, is a large proportion of births a favourable symptom. In the average state of a well-peopled territory there cannot be a worse sign than a large proportion of births, nor a better sign than a small proportion. A small proportion of births is a decided proof of a very small mortality, since the supply always equals the demand for population. In despotic, miserable, or naturally unhealthy countries, the proportion of births to the whole population will generally be found very great. In Scotland emigration is a potent cause of depopulation, but any thinning out from this cause is quickly neutralised by an increased proportion of births. In Ireland the details of population fluctuations are little known; but the cheapness of potatoes, and the ignorance and depressed, indifferent state of the people, have encouraged marriage to such a degree that the population is pushed much beyond the resources of the country, and the consequence, naturally, is that the lower classes of the people are in the most impoverished and miserable state. The checks to the population are, of course, chiefly of the positive kind, and arise from the diseases caused by squalid poverty. To these positive checks have of late years been added the vice and misery of civil war, and of martial law. _II.--Population and the Subsistence Level_ That the checks which have been mentioned are the immediate causes of the slow increase of population, and that these checks result principally from an insufficiency of subsistence will be evident from the comparative rapid increase which has invariably taken place whenever, by some sudden enlargement in the means of subsistence, these checks have been in any considerable degree removed. Plenty of rich land to be had for little or nothing is so powerful a cause of population as generally to overcome all obstacles. The abundance of cheap and profitable land obtained by the colonists in English North America resulted in a rapid increase of population almost without parallel in history. Such an increase does not occur in Britain, and the reason to be assigned is want of food. Want of food is certainly the most efficient of the three immediate checks to population. Population soon increases after war and disease and convulsions of nature, because the food supply is more than adequate for the diminished numbers; but where food is deficient no increase of population can occur. Since the world began the causes of population and depopulation have been probably as constant as any of the laws of nature with which we are acquainted.