(In instances of this kind the powers of the earth appear to be fully equal to answer it the demands for food that can be made upon it by man. But we should be led into an error if we were thence to suppose that population and food ever really increase in the same ratio. The one is still a geometrical and the other an arithmetical ratio, that is, one increases by multiplication, and the other by addition. Where there are few people, and a great quantity of fertile land, the power of the earth to afford a yearly increase of food may be compared to a great reservoir of water, supplied by a moderate stream. The faster population increases, the more help will be got to draw off the water, and consequently an increasing quantity will be taken every year. But the sooner, undoubtedly, will the reservoir be exhausted, and the streams only remain. When acre has been added to acre, till all the fertile land is occupied, the yearly increase of food will depend upon the amelioration of the land already in possession;and even this moderate stream will be gradually diminishing. But population, could it be supplied with food, would go on with unexhausted vigour, and the increase of one period would furnish the power of a greater increase the next, and this without any limit.)These facts seem to shew that population increases exactly in the proportion that the two great checks to it, misery and vice, are removed, and that there is not a truer criterion of the happiness and innocence of a people than the rapidity of their increase. The unwholesomeness of towns, to which some persons are necessarily driven from the nature of their trades, must be considered as a species of misery, and every the slightest check to marriage, from a prospect of the difficulty of maintaining a family, may be fairly classed under the same head. In short it is difficult to conceive any check to population which does not come under the description of some species of misery or vice.
The population of the thirteen American States before the war was reckoned at about three millions. Nobody imagines that Great Britain is less populous at present for the emigration of the small parent stock that produced these numbers. On the contrary, a certain degree of emigration is known to be favourable to the population of the mother country. It has been particularly remarked that the two Spanish provinces from which the greatest number of people emigrated to America, became in consequence more populous. Whatever was the original number of British emigrants that increased so fast in the North American Colonies, let us ask, why does not an equal number produce an equal increase in the same time in Great Britain? The great and obvious cause to be assigned is the want of room and food, or, in other words, misery, and that this is a much more powerful cause even than vice appears sufficiently evident from the rapidity with which even old states recover the desolations of war, pestilence, or the accidents of nature. They are then for a short time placed a little in the situation of new states, and the effect is always answerable to what might be expected. If the industry of the inhabitants be not destroyed by fear or tyranny, subsistence will soon increase beyond the wants of the reduced numbers, and the invariable consequence will be that population which before, perhaps, was nearly stationary, will begin immediately to increase.
The fertile province of Flanders, which has been so often the seat of the most destructive wars, after a respite of a few years, has appeared always as fruitful and as populous as ever.
Even the Palatinate lifted up its head again after the execrable ravages of Louis the Fourteenth. The effects of the dreadful plague in London in 1666 were not perceptible fifteen or twenty years afterwards. The traces of the most destructive famines in China and Indostan are by all accounts very soon obliterated.10It may even be doubted whether Turkey and Egypt are upon an average much less populous for the plagues that periodically lay them waste. If the number of people which they contain be less now than formerly, it is, probably, rather to be attributed to the tyranny and oppression of the government under which they groan, and the consequent discouragements to agriculture, than to the loss which they sustain by the plague. The most tremendous convulsions of nature, such as volcanic eruptions and earthquakes, if they do not happen so frequently as to drive away the inhabitants, or to destroy their spirit of industry, have but a trifling effect on the average population of any state. Naples, and the country under Vesuvius, are still very populous, notwithstanding the repeated eruptions of that mountain. And Lisbon and Lima are now, probably, nearly in the same state with regard to population as they were before the last earthquakes.
