Now this physical department has ever proved the vulnerable portion of false religions,--the portion which, if I may use the metaphor, their originators could not dip in the infernal river. The ability of drawing the line, in the early and ignorant ages of the world, between what man can of himself discover and what he cannot, is an ability which man cannot possibly possess. The ancient Chaldeans, who first watched the motions of the planets, could not possibly have foreseen, that while on the one hand men would be one day able of themselves to measure and weigh these bodies, and to determine their distances from the earth and from each other, men might never be able of themselves to demonstrate the fact of their authorship, or to discover the true character of their author. Nay, if they could have at all thought on the subject, the latter would have seemed to them by much the simpler discovery of the two. To know at such a time what was in reality discoverable and what was not, would be to know by anticipation what is not yet known,--the limits of all human knowledge. It would be to trace a line non-existent at the period, and untraceable, in the nature of things, until the history of the human race shall be completed. It was held by even the sagacious Socrates, that men cannot arrive at any certainty in questions respecting the form or motion of the earth, or the mechanism of the heavens; and so he set himself to elucidate what he deemed much simpler matters,--to prove, for instance, as we find in the Phedon, that human souls existed ere they came to inhabit their mortal bodies, and retained faint recollections of great misfortunes that had overtaken them ere their embodiment as men, and of sufferings to which they had been subjected in a primevous state. And lacking this ability of distinguishing between the naturally discoverable and what cannot be naturally discovered, the originators of the old mythologic beliefs obtruded into provinces in which ultimately the lawless nature of the obtrusion could not fail to be detected; and thus, by making their false science a portion of their false religion, they created what was afterwards to prove its weakest and most vulnerable part. We absolutely know that the course at present pursued by enlightened Christian missionaries in India is to bring scientific truth into direct antagonism with the monstrously false science of the pretended revelations of Parseeism, Brahminism, and Buddhism; and that by this means the general falsity of these systems has been so plainly shown, that it has become a matter of doubt whether a single educated native of any considerable ability in reality believes in them. They seem to have lost their hold of all the minds capable of appreciating the weight and force of scientific evidence.