be guided by the
same traditions.

[Illustration: Fig. 9. "Spotting" a single line on a page so that it
makes an interesting division of space. There are 2 parts of white space
above and 3 parts below.]

[Illustration: Fig. 10. Placing a single line so that it will appear to
be centered. The dotted lines show the mathematical center of the
vertical side. The straight lines show the center of the type line.]

The most simple application of proportion to the division of a printed
page occurs when a single type line or compact group of lines is to be
placed on the page (Fig. 9).

It is unfortunate that it is so easy to divide space mechanically in a
type page by using identical measures of furniture or slugs above and
below. When, in certain instances (as in a business card), tradition
demands that a line be "centered" vertically, it will be found that the
exact centering of the line will make it appear a bit low. An optical
illusion demands that such a line be raised slightly if it is to appear
in the vertical center (Fig. 10). This apparent center is called "the
optical center."

The same condition makes it necessary when an apparent square is to be
used that the width of the "square" be slightly greater than the height.
(Fig. 11.)

[Illustration: Fig. 11. A true square above and an optically corrected
square below. Psychologists explain that the eyes find it more difficult
to judge the length of vertical lines, hence are inclined to exaggerate
them.]

_Balance_

The physical equilibrium which exists in the balanced "seesaw" of our
childhood and the optical balance which is the result of the proper
adjustment of masses within the confining edges of a design are similar,
in that each is an equalizing of forces of attraction. In the former the
force is gravity; in the latter, the attraction to the eye, which varies
with the size and tone of the mass. While the force of gravity usually
brings balancing masses to a horizontal alignment, optical balance may
bring the masses in a design into equilibrium on any desired line,
horizontal, vertical, or diagonal.

The attraction which a mass possesses varies directly with its size and
tone. Thus a mass of four square inches, solid black, will be twice as
strong in attraction value as a mass of two square inches, solid black.
It will also be twice as strong in attraction value as a mass of four
square inches, neutral gray (the gray being half the value of black).