absolute sense; all physical and moral causes, and all the effects which flow from them, are comprised and balanced within certain limits, more or less extended, but never so large as to destroy the equilibrium. As the whole universe is in a state of perpetual motion, and as all the forces of matter act against and counter-balance each other, so every thing is brought about in a kind of oscillation, to the middle points of which we refer the ordinary course of Nature, and whose extremes are the furthest removed from that course. In effect, therefore, we find that an excess of fecundity, either in animals or vegetables, is the usual fore-runner of sterility. Plenty and scarcity present themselves so alternately, and often follow so close upon each other, that a tolerable judgment may be formed of the product of one year by that of the preceding. The apple, plum, oak, beech, and indeed most fruit and forest trees, do not bear plentifully two years together. So likewise it is with caterpillars, May-bugs, flies, field mice, and many other animals, who if they multiply to excess one year, they will produce but a very small number the next. What, indeed, would become of all the fruits of the earth, of the most useful animals, or even of man himself, if these insects were to be proportionally increased after a fertile season? But no; the causes of destruction and sterility immediately follow those of an excessive multiplication. Independent of contagion, a necessary consequence of too great a mass of living matter assembled in one place, there are in every species, certain causes of death, as we shall hereafter have occasion to mention, and which are sufficient to counter-balance any preceding excess of fecundity. I must again observe that this is not to be taken in an absolute or strict sense, especially with respect to those species which do not remain entirely in a state of nature. Those which man takes care to rear are more abundant than they otherwise would be; but as his attention has its limits, so the increase which flows from it has long since been confined by unalterable bounds; and though in civilized countries, the human species and domestic animals, are more numerous than in other climates, they are never so to excess; because the very power which calls them into existence, destroys them when they become troublesome. [J] We were at first inclined to combat this position of our learned author, with those reasons, founded upon facts, which may be adduced against it; but he has himself so completely replied to it at the end of his dissertation upon wild animals, page 26 of this volume, that any thing further than repeating his own observation must be unnecessary; for he there says, that, "in _process of time, we may reasonably suppose the surface of the earth will be equally inhabited_," which is surely impossible without considerable increase.