Page:Two Lectures on the Checks to Population.pdf/19

13 of life. Though however not accurately geometrical, it yet preserves those main features of a geometrical progression, which are essential with regard to practical considerations, viz. that the increase of one period furnishes the power of a greater increase in the next, and this without any limit.

The third rate, or the actual progression, is of course the most variable of all, being inﬂuenced by the greatest variety of causes. It is observable, that, while the checks, which produce the difference between the first rate and the second, have the property of retarding, and of taking away a part of the original rate of progression, still they are not connected with any limitation of its range, and their intensity is not necessarily increased in consequence of any actual increase of number. But the checks, which cause the difference between the second rate and the third, are subject to variations in intensity dependent on the actual range. They not only retard, but they limit also. In short, the difference between the first and second class of checks, to which I am here alluding, is, that those of the first class, though they lessen