The following Lectures are printed, as far as possible, just as they were delivered. Here and there a sentence which seemed obscure has been mended, and the passages which had not been previously written, have been, of course imperfectly, supplied from memory. But I am well assured that nothing of any substantial importance which was said in the lecture-room, is either omitted, or altered in its signification; with the exception only of a few sentences struck out from the notice of the works of Turner, in consequence of the impossibility of engraving the drawings by which they were illustrated, except at a cost which would have too much raised the price of the volume. Some elucidatory remarks have, however, been added at the close of the second and fourth Lectures, which I hope may be of more use than the passages which I was obliged to omit.