Mr. Malthus clearly exposed the error of such teaching. He showed that, such is the immense power of increase in the human family, it is probable that, were food plentiful enough, population might double in some fifteen years, or even less. With incredible assiduity he read and examined ancient history and the statistics of European countries and their colonies, for the confirmation of his theory. He found, for example, that after the great pestilences which had from time to time ravaged European states, the surviving population had been so well fed and housed that it had been enabled to replace the blanks left by deaths usually in a very few years—in twenty years in several instances. Turning to the colonies of Great Britain in the United States, Malthus confirmed what the great pioneer of all progress in political economy, Adam Smith, had noted, namely, that the colonists of those States had doubled since their settlement in considerably less than twenty-five years in some cases, without taking into account any fresh immigration. In an article in the Encyclopædia Britannica, written by Malthus, he gives most accurately the figures of the doubling of the population of the United States from the year 1790 until 1820; and shows, from statistics, that very few immigrants had arrived from Europe during this period. Making ample allowance for the contingent for such immigration, Malthus showed that, from 1790 to 1815, the population of the States had more than doubled. Hence he was led to the following expression:—“Population, when unchecked, goes on doubling every twenty-five years, or increases in a geometrical ratio.” He next shows that the tendency of agricultural produce fit for the food of man is to increase very much more slowly than man could increase. This has been termed the “law of agricultural increase,” and is very easily understood by taking an example. Let us grant that the average quantity of wheat that can be grown at present on an acre of ground in England is thirty bushels. It would be clearly impossible to suppose that in 25 years 60 bushels per acre could be produced; in 50 years, 120 bushels, and so on. Whereas, the tendency of population to double in from 12 to 25 years is clear enough, when it is remembered that the human female commences to be capable of reproduction at about fifteen and continues so until forty-five, in this climate. Were European women to marry as early as the Hindoo women do, there would be a possibility, if food were forthcoming, of a doubling of the population in some fifteen years or less.