Abernethy stated nothing as facts but which were demonstrably such; and with regard to any hypotheses which he employed in aid of explaining them, he observed those conditions which philosophers agree on as necessary, whether the hypotheses be adopted or otherwise. He did not do even this, but for the very legitimate object of explaining the views of the man on whose labours he was discoursing. When those views of Mr. Hunter, which had been thus set forth and illustrated, were attacked, he defended them with his characteristic ability; and although we will not undertake to say that the defence contains no single passage that might not as well have been omitted, we are not aware that, from the beginning to the end, it is charged with a single paragraph that does not fall fairly within the limits that the most stringent would prescribe to scientific controversy. The discussion of abstract principles is generally unprofitable. We think few things more clear than that we know not the intrinsic nature of _any_ abstract principle; and although it would be presumptuous to say we never shall, yet we think it impossible for any reflecting student in any science to avoid perceiving that there are peculiar relations between the _laws_ of nature and the human capacity, which most emphatically suggest that the study of the one is the _proper business_, and the _prescribed limit_ to the power, of the other. Still, the poverty of language is such, as regards the expression of natural phenomena, that necessity has obliged us to clothe the forces in nature with some attribute sufficiently in conformity with our ideas to enable us to give them an intelligible expression; and, whether we talk of luminous particles, ethereal undulations, electric or magnetic fluids, matter of heat, &c. we apprehend that no one now means more than to convey an intellectually tangible expression, of certain _forces_ in nature, of which he desires to discourse; in order to describe the _habitudes_ they observe, or the laws which they obey. This is all we think it necessary to say on the scientific conduct of the argument by Abernethy.