IIQ 
ball ; 
between 
the 
centre 
of 
the 
illumination 
anid the circle of the ball, 
where the illumination 
reaches its extremity, lies what may be called 
the transparent tint; and between it and the 
dark 
of 
side 
the 
ball 
lies 
the 
aerial 
middle 
tint. The point of darkness, the extreme of 
shade, is diametrically opposite to the focus of 
illumination, between which and the mrial tint 
lies the tint of 
reflection. 
If 
the 
ball 
rests on 
a plain, it will throw a shadow equal in length 
to one diameter and a quarter of the ball. That 
shadow will be darker than the shade on the ball, 
and the darkest part will be where the plain and 
ball come in contact with each other. 
" This simple experiment, whether performed 
in the open _sun-shine, or with artificial illumin- 
ation, will lead you to the true principles of light 
and shade over all objects in nature, whether 
mountains, clouds, rocks, trees, single figures, 
or groups of figures. It would therefore {be of 
great use, when you are going to give lightand 
shade to any object, first to make the experiment 
of the ball, and in giving that light and shade, 
followarthe lessons with which it will furnish you.