THE ELEMENTS OF DRAWING. [letter hi.
precisely at the spot where it comes against a dark
hill, and similarly treat all her masses of shade and
colour, is so great, that if you only follow her closely,
every one who looks at your drawing with attention
will think that you have been inventing the most
artificially and unnaturally delightful interchanges of
shadow that could possibly be devised by human wit.
You will find this law of interchange insisted upon
at length by Prout in his Lessons on Light and
Shade: it seems, of all his principles of composition,
to be the one he is most conscious of; many others
he obeys by instinct, but this he formally accepts
and forcibly declares.
The typical purpose of the law of interchange is,
of course, to teach us how opposite natures may be
helped and strengthened by receiving each, as far as
they can, some impress or reflection, or imparted
power, from the other.
8. THE LAW OF CONSISTENCY.
It is to be remembered, in the next place, that
while contrast exhibits the characters of things, it