other to see how far they lent themselves to description by
substitutional symmetry. Thus: in B. van der Helst's "Portrait
of Paul Potter," the head of the subject is entirely to left
of the central line, as also his full face and frontward glance.
His easel is right, his body turned sharply to right, and both
hands, one holding palette and brushes, are stretched down to
right. Thus the greater mass is to the left, and the general
direction of line is to the right; elements of interest in the
head, left; in implements, right. This may be schematized in
the equation (Lt.)M.+I.=(Rt.)I.+L.

Pieter de Hooch, "The Card-Players," in Buckingham Palace,
portrays a group completely on the right of the central line,
all facing in to the table between them. Directly behind them
is a high light window, screened, and high on the wall to the
extreme right are a picture and hanging cloaks. All goes to
emphasize the height, mass, and interest of the right side.
On the left, which is otherwise empty, is a door half the
height of the window, giving on a brightly lighted courtyard,
from which is entering a woman, also in light clothing. The
light streams in diagonally across the floor. Thus, with all
the "weight" on the right, the effect of this deep vista on
the left and of its brightness is to give a complete balance,
while the suggestion of line from doorway and light makes,
together with the central figure, a roughly outlined V, which
serves to bind together all the elements. Equation, (Lt.)V.+I.
=(Rt.)M.+I.

The thousand pictures on which the study was based<1> were
classified for convenience into groups,--Religious, Portrait,