It was not, however, to point out to you the advantage which arises to the study of our mental frame, from the comparative facility as to the circumstances attending it, that I have led your attention to the difference, in this respect, of the physics of mind and matter. It was to show,--what is of much more importance,--how essential a right view of the science of mind is to every other science, even to those sciences, which superficial thinkers might conceive to have no connexion with it; and how vain it would be to expect, that any branch of the physics of mere matter could be cultivated to its highest degree of accuracy and perfection, without a due acquaintance with the nature of that intellectual medium, through which alone the phenomena of matter become visible to us, and of those intellectual instruments, by which the objects of every science, and of every science alike, are measured, and divided, and arranged. We might almost as well expect to form an accurate judgment, as to the figure, and distance, and colour of an object, at which we look through an optical glass, without paying any regard to the colour and refractory power of the line itself. The distinction of the sciences and arts, in the sense in which these words are commonly understood, is as just as it is familiar; but it may be truly said, that, in relation to our power of discovery, science is itself an art, or the result of an art. Whether, in this most beautiful of processes, we regard the mind as the instrument or the artist, it is equally that by which all the wonders of speculative, or practical knowledge, are evolved. It is an agent operating in the production of new results, and employing for this purpose the known laws of thought, in the same manner as, on other occasions, it employs the known laws of matter. The objects, to which it may apply itself, are indeed various, and, as such, give to the sciences their different names. But, though the objects vary, the observer and the instrument are continually the same. The limits of the powers of this mental instrument, are not the limits of its powers alone; they are also the only real limits, within which every science is comprehended. To the extent which it allows, all those sciences, physical or mathematical, and all the arts which depend on them, may be improved; but, beyond this point, it would be vain to expect them to pass; or rather, to speak more accurately, the very supposition of any progress beyond this point would imply the grossest absurdity; since human science can be nothing more than the result of the direction of human faculties to particular objects. To the astronomer, the faculty by which he calculates the disturbing forces that operate on a satellite of Jupiter, in its revolution round its primary planet, is as much an instrument of his art, as the telescope by which he distinguishes that almost invisible orb; and it is as important, and surely as interesting, to know the real power of the