(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.