It will be remembered how signally, in the question in the General Assembly of the Church of Scotland, as to Sir John Leslie's professorship, the argument of irreligion was retaliated; and it was shown that, in the theory of an existing machinery in nature enabling the universe to proceed in its regular course, the cause having within it the adequate power for producing its effect, the omnipresence of a Deity was dispensed with, and there was substituted for the all-pervading influence of a superior wisdom, a mere material machine, having within itself the elements of its own regular motion. Thus, in instances where writers have claimed credit for having aided the cause of religion by carrying out the principles of natural theology, this merit has in many cases, and among certain classes of devout religious thinkers, been sternly denied them; and it has been said that their labours are rather adverse than favourable to revealed religion, because, through their tendency to make people believe in an established order in nature, by which causes produce their effects according to a fixed system, they have the effect of making mankind forget the existence of a revealed, omnipresent Deity, whose all-competent superintendence regulates the world, and they supply a religion independent of the religion of revelation. Perhaps in this little history we may find an illustration of the view, that the greatest service which the Treatise has done to philosophy is that purely incidental one of teaching human reason its own weakness--of showing how easily the noblest fabric of human thought may be undermined, by a destroying agency of power not greater than that of the constructive genius which has raised it. In this respect it has done to philosophy the invaluable service of teaching philosophers their own fallibility. In all the departments of thought, and not only in the world of thought but in that of action, the spirit of human infallibility is the greatest obstacle to truth and goodness. Whether it appear to protect a system which the thinker has framed for himself, or assume the more modest shape of maintaining, that among conflicting systems he has made choice of that which is absolutely and certainly right, while all others which in any way differ from it are as absolutely and certainly wrong; this offspring of the pride of human intellect is an equally dangerous enemy of human improvement; and to have contributed to its downfal is of itself no small achievement for one mind.