shadow being regarded as the effect of internal causes acting on that part of the retina, and not of the impression of coloured rays from without. This explanation is the one adopted by Rumford, Goethe, Grotthuss, Brandes, Tourtual, Pohlmann, and most authors who have studied the subject."71
In the Historical Part the author gives an account of a scarce French work, "Observations sur les Ombres Colorées," Paris, 1782. The writer72 concludes that "the colour of shadows is as much owing to the light that causes them as to that which (more faintly) illumines them."
NOTE E.—Par. 69.
This opinion of the author is frequently repeated (201, 312, 591), and as it seems at first sight to be at variance with a received principle of art, it may be as well at once to examine it.
In order to see the general proposition in its true point of view, it will be necessary to forget the arbitrary distinctions of light and shade, and to consider all such modifications between highest brightness and absolute darkness only as so many lesser degrees of light.73 The author, indeed, by the word shadow, always understands a lesser light.
The received notion, as stated by Du Fresnoy,74 is much too positive and unconditional, and is only true when we understand the "displaying" light to comprehend certain degrees of half or reflected light, and the "destroying" shade to mean the intensest degree of obscurity.
There are degrees of brightness which destroy colour as well as degrees of darkness.75 In general, colour resides in a mitigated