were it not that the error they are built upon, hath been a continual blight to the growth of the art, by misguiding both the proficient, and the encourager; and often compelling the former, contrary to his judgment, to imitate the damaged hue of decayed pictures; so that when his works undergo the like injuries, they must have a double remove from nature; which puts it in the power of the meanest observer to see his deficiencies. Whence another absurd notion hath taken rise, viz. that the colours now-a-days do not stand so well as formerly; whereas colours well prepared, in which there is but little art or expence, have, and will always have, the same properties in every age, and without accidents, as damps, bad varnish, and the like (being laid separate and pure,) will stand and keep together for many years in defiance of time itself. In proof of this, let any one take a view of the cieling at Greenwich-hospital, painted by Sir James Thornhil, forty years ago, which still remains fresh, strong and clear as if it had been finished but yesterday: and altho' several french writers have so learnedly, and philosophically proved, that the air of this island is too thick, or--too something, for the genius of a painter; yet France in all her palaces can hardly boast of a nobler, more judicious, or richer performance of its kind. Note, the upper end of the hall where the royal family is painted, was left chiefly to the pencil of Mr. Andrea a foreigner, after the payment originally agreed upon for the work was so much reduced, as made it not worth Sir James's while to finish the whole with his own more masterly hand. Upon the whole of this account we find, that the utmost beauty of colouring depends on the great principle of varying by all the means of varying, and on the proper and artful union of that variety; which may be farther proved by supposing the rules here laid down, all or any part of them reversed. I am apt to believe, that the not knowing nature's artful, and intricate method of uniting colours for the production of the variegated composition, or prime tint of flesh, hath made colouring, in the art of painting, a kind of mystery in all ages; insomuch, that it may fairly be said, out of the many thousands who have labour'd to attain it, not above ten or twelve painters have happily succeeded therein, Corregio (who lived in a country-village, and had nothing but the life to study after) is said almost to have stood alone for this particular excellence. Guido, who made beauty his chief aim, was always at a loss about it. Poussin scarce ever obtained a glimpse of it, as is manifest by his many different attempts: indeed France hath not produced one remarkably good colourist[19].