The harmony in color which
corresponds to this, and leaves nothing for the eye to desire, is, of
course, the light that nature is full of--sunlight. White light is then
the fundamental chord of color, and it is constructed on the red as the
tonic, consisting of red, yellow, and blue, the 1st, 3d, and 5th of the
solar spectrum.

This little analogy is suggestive, but its development is striking.

The diatonic scale in music, determined by calculation and actual
experiment on vibrating chords, stands as follows. It will be easily
understood by musicians, and its discussion appears in most treatises on
acoustics:

Do Re Mi Fa Sol La Ti Do

C, D, E, F, G, A, B, C, &c.

1 9/8 5/4 4/3 3/2 5/3 15/8 2.

The intervals, or relative pitches of the notes to the tonic C, appear
expressed in the fractions, which are determined by assuming the wave
length or amount of vibration of C as unity, and finding the ratio of
the wave length of any other note to it. The value of an interval is
therefore found by dividing the wave length of the graver by that of the
acuter note, or the number of vibrations of the acuter in a given time
by the corresponding number of the graver. These fractions, it is seen,
comprise the simplest ratios between the whole numbers 1 and 2, so that
in this scale are the simple and satisfactory elements of harmony in
music, and everybody knows that it is used as such. Now nature exposes
to us a scale of color to which we have adverted; it is thus:

Red, Orange, Yellow, Green, Blue, Indigo, Violet.

Let us investigate this, and see if her science is as good as mortal
penetration; let us see if she too has hit upon the simplest fractions
between 1 and 2, for a scale of 7. We can determine the relative pitch
of any member of this scale to another, easily, as the wave lengths of
all are known from experiment.

The waves of red are the longest; it corresponds, then, to the tonic.
Let us assume it as unity, and deduce the pitch of orange by dividing
the first by the second.

The length of a red wave is 0.0000266 inches; the length of an orange
wave is 0.0000240 inches; the fraction required then is 266/240;
dividing both members of this expression by 30, it reduces to 9/8,
almost exactly. This is encouraging. We find a remarkable coincidence in
ratio, and in elements which occupy the same place on the corresponding
scales. Again, the length of a yellow wave is 0.00002