The first volume was the expansion of a reply to a magazine article; and was not begun because I then thought myself qualified to write a systematic treatise on Art; but because I at least knew, and knew it to be demonstrable, that Turner was right and true, and that his critics were wrong, false, and base. At that time I had seen much of nature, and had been several times in Italy, wintering once in Rome; but had chiefly delighted in northern art, beginning, when a mere boy, with Rubens and Rembrandt. It was long before I got quit of a boy's veneration for Rubens' physical art-power; and the reader will, perhaps, on this ground forgive the strong expressions of admiration for Rubens, which, to my great regret, occur in the first volume. Finding myself, however, engaged seriously in the essay, I went, before writing the second volume, to study in Italy; where the strong reaction from the influence of Rubens threw me at first too far under that of Angelico and Raphael, and, which was the worst harm that came of that Rubens influence, blinded me long to the deepest qualities of Venetian art; which, the reader may see by expressions occurring not only in the second, but even in the third and fourth volumes, I thought, however powerful, yet partly luxurious and sensual, until I was led into the final inquiries above related. These oscillations of temper, and progressions of discovery, extending over a period of seventeen years, ought not to diminish the reader's confidence in the book. Let him be assured of this, that unless important changes are occurring in his opinions continually, all his life long, not one of those opinions can be on any questionable subject true. All true opinions are living, and show their life by being capable of nourishment; therefore of change. But their change is that of a tree--not of a cloud. In the main aim and principle of the book, there is no variation, from its first syllable to its last. It declares the perfectness and eternal beauty of the work of God; and tests all work of man by concurrence with, or subjection to that. And it differs from most books, and has a chance of being in some respects better for the difference, in that it has not been written either for fame, or for money, or for conscience-sake, but of necessity. It has not been written for praise. Had I wished to gain present reputation, by a little flattery adroitly used in some places, a sharp word or two withheld in others, and the substitution of verbiage generally for investigation, I could have made the circulation of these volumes tenfold what it has been in modern society. Had I wished for future fame, I should have written one volume, not five. Also, it has not been written for money. In this wealth-producing country, seventeen years' labor could hardly have been invested with less chance of equivalent return.