One effect of Goethe's theory has been to invite the attention of scientific men to facts and appearances which had before been unnoticed or unexplained. To the above cases may be added the very common, but very important, fact in painting, that a light warm colour, passed in a semi-transparent state over a dark one, produces a cold, bluish hue, while the operation reversed, produces extreme warmth. On the judicious application of both these effects, but especially of the latter, the richness and brilliancy of the best-coloured pictures greatly depends. The principle is to be recognised in the productions of schools apparently opposite in their methods. Thus the practice of leaving the ground, through which a light colour is apparent, as a means of ensuring warmth and depth, is very common among the Dutch and Flemish painters. The Italians, again, who preferred a solid under-painting, speak of internal light as the most fascinating quality in colour. When the ground is entirely covered by solid painting, as in the works of some colourists, the warmest tints in shadows and reflections have been found necessary to represent it. This was the practice of Rembrandt frequently, and of Reynolds universally, but the glow of their general colour is still owing to its being repeatedly or ultimately enriched on the above principle. Lastly, the works of those masters who were accustomed to paint on dark grounds are often heavy and opaque; and even where this influence of the ground was overcome, the effects of time must be constantly diminishing the warmth of their colouring as the surface becomes rubbed and the dark ground more apparent through it. The practice of painting on dark grounds was intended by the Carracci to compel the students of their school to aim at the direct imitation of the model, and to acquire the use of the brush; for the dark ground could only be overcome by very solid painting. The result answered their expectations as far as dexterity of pencil was concerned, but the method was fatal to brilliancy of colour. An intelligent writer of the seventeenth century[5] relates that Guido adopted his extremely light style from seeing the rapid change in some works of the Carracci soon after they were done. It is important, however, to remark, that Guido's remedy was external rather than internal brilliancy; and it is evident that so powerless a brightness as white paint can only acquire the splendour of light by great contrast, and, above all, by being seen through external darkness. The secret of Van Eyck and his contemporaries is always assumed to consist in the vehicle (varnish or oils) he employed; but a far more important condition of the splendour of colour in the works of those masters was the careful preservation of internal light by painting thinly, but ultimately with great force, on white grounds. In some of the early Flemish pictures in the Royal Gallery at Munich, it may be observed,