y white, we want a contrasting
shadow somewhere; and get it, under our piece of decrepitude. This
shade, with the tiles of the wall below, forms another pointed mass,
necessary to the first by the law of repetition. Hide this inferior
angle with your finger, and see how ugly the other looks. A sense of the
law of symmetry, though you might hardly suppose it, has some share in
the feeling with which you look at the battlements; there is a certain
pleasure in the opposed slopes of their top, on one side down to the
left, on the other to the right. Still less would you think the law of
radiation had anything to do with the matter: but if you take the
extreme point of the black shadow on the left for a centre and follow
first the low curve of the eaves of the wall, it will lead you, if you
continue it, to the point of the tower cornice; follow the second curve,
the top of the tiles of the wall, and it will strike the top of the
right-hand battlement; then draw a curve from the highest point of the
angle battlement on the left, through the points of the roof and its
dark echo; and you will see how the whole top of the tower radiates from
this lowest dark point. There are other curvatures crossing these main
ones, to keep them from being too conspicuous. Follow the curve of the
upper roof, it will take you to the top of the highest battlement; and
the stones indicated at the right-hand side of the tower are more
extended at the bottom, in order to get some less direct expression of
sympathy, such as irregular stones may be capable of, with the general
flow of the curves from left to right.

You may not readily believe, at first, that all these laws are indeed
involved in so trifling a piece of composition. But as you study longer,
you will discover that these laws, and many more, are obeyed by the
powerful composers in every _touch_: that literally, there is never a
dash of their pencil which is not carrying out appointed purposes of
this kind in twenty various ways at once; and that there is as much
difference, in way of intention and authority, between one of the great
composers ruling his colours, and a common painter confused by them, as
there is between a general directing the march of an army, and an old
lady carried off her feet by a mob.

7. THE LAW OF INTERCHANGE.

Closely connected with the law of contrast is a law which enforces the
unity of opposite things, by giving to each a portion of the character
of the