The arresting power of the right angle exists at each corner of a rectangular picture, where the vertical sides meet the horizontal base, and this presents a difficulty, because you do not wish the spectator’s attention drawn to the corners, and this dramatic combination of lines always attracts the eye.  A favourite way of getting rid of this is to fill them with some dark mass, or with lines swinging round and carrying the eye past them, so that the attention is continually swung to the centre of the picture.  For lines have a power of directing the attention, the eye instinctively running with them, and this power is of the greatest service in directing the spectator to the principal interest.

It is this trouble with the corners that makes the problem of filling a square so exacting.  In an ordinary rectangular panel you have a certain amount of free space in the middle, and the difficulty of filling the corners comfortably does not present itself until this space is arranged for.  But in a square, the moment you leave the centre you are in one or other of the corners, and the filling of them governs the problem much more than in the case of other shapes.  It is a good exercise for students to give themselves a square to fill, in order to understand this difficulty and learn to overcome it.

Other lines that possess a direct relation to a rectangular shape are the diagonals.  Many compositions that do not hang on a vertical or horizontal basis are built on this line, and are thus related to the bounding shape.

[Illustration:  Plate XXXVI.

THE SURRENDER OF BREDA VELAZQUEZ (PRADO)

Photo Anderson]

When vertical, horizontal, or diagonal lines are referred to, it must not be assumed that one means in all cases naked lines.  There is no pure vertical line in a stone pine or cypress tree, nor pure horizontal line in a stretch of country, but the whole swing of their lines is vertical or horizontal.  And in the same way, when one speaks of a composition being hung upon a diagonal, it is seldom that a naked diagonal line exists in the composition, but the general swing is across the panel in harmony with one or other diagonal.  And when this is so, there is a unity set up between the design and its boundaries.  A good instance of vertical, horizontal, and diagonal lines to unite a picture is Velazquez’s “The Surrender of Breda,” here reproduced.  Note the vertical chord in the spears on the left, continued in the leg of the horse and front leg of the figure receiving the key, and the horizontal line made by the dark mass of distant city, to be continued by the gun carried over the shoulder of the figure with the slouch hat behind the principal group.  Velazquez has gone out of his way to get this line, as it could hardly have been the fashion to carry a gun in this position, pointing straight at the head of the man behind.  Horizontal lines also occur in the sky and distant