y prominent because of their blackness. They
do not seem harmonious with the gray tone of the others. If we replace
them with other pieces gray in color, as in Fig. 5, the result will be a
more pleasing relationship of tone throughout the design. Thus we have
made a simple demonstration of _tone harmony_.

If our pieces of paper were of various colors we could make another
arrangement to express a _color harmony_. The problem of color, however,
has so many phases that it is considered separately in this series.

If rhythm is to give us a "regular recurrence" of various features of a
design, it will be possible to choose a combination of pieces of paper
which will show a rhythmic arrangement, Fig. 6. It will be noticeable
here that the shapes occur in successive groups which repeat an idea.

We may also arrange a series of pieces in which the tones are rhythmic,
progressing from light to dark in repeated groups. This will be a simple
example of _tone rhythm_, Fig. 7.

Summing up the experiment thus far the following definitions may be
noted:

_Shape harmony_ will exist when masses similar in contour or shape are
used to form a design.

_Tone harmony_ results from the use of tones in a design which carry a
feeling of relationship.

[Illustration: Fig. 4. Units selected from Fig. 3, having a common
similarity of shape. But they are not harmoniously related in tone.]

[Illustration: Fig. 5. The same shapes used in Fig. 4, substituting
equal tones of gray as needed to produce harmony throughout.]

[Illustration: Fig. 6. Simple development of shape and measure rhythm
such as might occur on a printed page. Masses should be related in
measure as well as in shape.]

[Illustration: Fig. 7. Simple illustration of tone rhythm as it may
occur on a type page. The tones progress from the white of the margins
through the light gray masses of type, to the darker grays of
decorations.]

_Shape rhythm_ is the regular recurrence of similar shapes in a design
or a rhythmic increase or decrease in the size of shapes used in a
design.

_Tone rhythm_ is a recurrence of similar tones or a regular progression
of related tones from light to dark or the reverse through a design.

The four qualities above are so closely related that there is often no
definite dividing line between them; indeed, a successful design will
embody them all.

_Proportion_

Our definition of proportion as a comparative relationship of size is so