4 INTRODUCTION. 
example ; and I remember, when a young student at the Royal 
Academy, to have painted from the hfe with nearly such a lesson 
from a worthy and most esteemed artist, who was at that time the 
visiting academician. It would therefore seem that light or shade 
on convex or concave subjects, or where shadow is, is also accom- 
panied with colours ; the smallest shade being compounded not 
only of light and shade, or black and white, but of many tints de- 
pending on the nature of that light; for mere black and white would 
give an unartist-like manner and coldness, which would be con- 
demned in general, even by the least discerning, although perhaps 
without knowing why. Light and shade or shades will be shown 
hereafter to have a greater effect than is usually understood, with 
regard to colours, and will, I have no doubt, be found useful in 
' many other respects. Light and dark, as a contrast, and for effect, is 
very ancient, and sufficiently attracted Laban's flocks under the care 
of Jacob*. 
Light is essential in colouring some things and bleaching others; 
and it was once a valuable secret, that to get the brightest carmine 
it should in the process of making be dried in the sun. Many 
chemical substances are changed by exposure to light ; oils become 
whiter. Perhaps even this effect may be assisted with the help of a 
contrasting shade, that the actions may be more forcibly directed on 
the object. Light, on an object when seen refracted by the prism, 
shows its colours ; which however do not affect the general local tint 
of the object which seems to reflect it, but rather depend upon the 
darks or shadows ; and broad flat masses of any coloured object do 
not appear changed excepting at the extremities, or where dark or 
shade seems to help to collect the coloured radii : thus it may be 
possible to make broad tints or narrow ones with such proportions of 
dark or shade as may be suited for many purposes of the utmost 
utility in tlie arts^ manufactures, agriculture, &c. 
* Genesis XXX. 37 to 41. 
