for this is clear to any one who conceives of an art of mobile color,
not as a moving picture show--a thing of quick-passing concrete
images, to shock, to startle, or to charm--but as a rich and various
language in which light, proverbially the symbol of the spirit, is
made to speak, through the senses, some healing message to the soul.
For such a consummation, "devoutly to be wished," natural forms--forms
abounding in every kind of association with that world of materiality
from which we would escape--are out of place; recourse must be had
rather to abstract forms, that is, geometrical figures. And because
the more remote these are from the things of sense, from knowledge and
experience, the projected figures of four-dimensional geometry would
lend themselves to these uses with an especial grace. Color without
form is as a soul without a body; yet the body of light must be
without any taint of materiality. Four-dimensional forms are as
immaterial as anything that could be imagined and they could be made
to serve the useful purpose of separating colors one from another,
as lead lines do in old cathedral windows, than which nothing more
beautiful has ever been devised.

Coming now to the consideration, not of differences, but similarities,
it is clear that a correspondence can be established between the
colors of the spectrum and the notes of a musical scale. That is,
the spectrum, considered as the analogue of a musical octave can
be subdivided into twelve colors which may be representative of
the musical chromatic scale of twelve semi-tones: the very word,
_chromatic_, being suggestive of such a correspondence between sound
and light. The red end of the spectrum would naturally relate to the
low notes of the musical scale, and the violet end to the high, by
reason of the relative rapidity of vibration in each case; for the
octave of a musical note sets the air vibrating twice as rapidly as