Colour-Music: The Art of Mobile Color/Chapter 6
CHAPTER VI
CONSTRUCTION OF COLOUR-ORGAN AND OTHER INSTRUMENTS
AS the qualities we have been examining are, to a great extent, common to both music and the new art, and as they are so numerous and carry us so far towards the same artistic aims and ideals, it would therefore seem reasonable to use musical precedents to some extent in laying the foundations of one form at least of colour-music.
Very possibly the buildings raised upon these foundations may, later on, be pulled down again and better ones erected in their places upon the solid concrete of newer experiences. Or perhaps, to use another figure, musical methods should be regarded as merely the scaffolding upon which the first arch is thrown across the chasm of the untried—but this matters little, they will have served their purpose and given us experience of how to build.
Almost all arts have been developed from others that preceded them, and we are beginning to see that what we supposed were absolutely new inventions in art are far fewer than we believed.
Greek architectural forms were developed from Egyptian and other Oriental styles; early Italian artists painted their Madonnas upon outlines which had come from Byzantium, and even the mediæval pointed arch may have been suggested by Arabic buildings.
We must walk before we can run, and as there is a sister art some few centuries older, perhaps it may be well for the composer in colour-music to accept her guidance to some extent in making his first steps.
Taking it for granted that something is to be gained by adopting musical methods for some forms of the new art, though they certainly will not be the only ones, let us see how this is possible.
In one of the principal instruments which
Part of the pneumatic "action" of a mobile colour instrument with keyboard.
I have designed and constructed and used largely for experimental work—which will be referred to in future as the Colour-Organ—this has been done as follows:
It will be well to make this arrangement a little clearer by considering, first, the division of the colour-octave.
Taking the lower red arbitrarily as corresponding with the middle C, the octave is divided thus. (See illustration.)
This division was obtained in the following way.
The complete spectrum-band, greatly lengthened by sufficient distance, was thrown upon the screen by two bisulphide of carbon prisms—the source of white light being an unenclosed arc-lamp. An opaque diaphragm was then interposed close to the screen with an extremely narrow slit in it, and the fine slice of colour rays passing through it was made to correspond in position on the spectrum-band and approximately as to its rate of vibration to the notes of the musical scale in their relative intervals.
The narrow ribbon of colour, thus cut off from the spectrum-band, was then accurately matched and apparatus designed for producing it in larger quantity in the colour-organ and placing it under the control of the corresponding musical note upon its keyboard. The keys of the colour-organ were then connected with suitable mechanism for allowing these several colours to appear on the screen 
Illustrating a colour phrase, in which the fourth note is gradually increased in strength by the swell pedal of the colour organ.
A swell pedal was also provided, and if moved in one direction the brilliancy and intensity of the colour is increased throughout the whole of the length of the scale, if in the other, the colour effect is made more tender. Another stop enables either softened or "staccato" productions of the colour upon the screen to be given.
It is, of course, quite clear that, in order to use an instrument provided with a keyboard like that just described, it is necessary to devise some method of musical notation. Any absolutely new method would bring with it various difficulties, the foremost among them being the necessity for the executant to learn the new method, and for any composer in mobile colour also to be familiar with it. It would seem, therefore, that there is a good deal to be said for the adoption of a method which is already in use. This decided the author to employ the ordinary musical system—at any rate for all the preliminary experiments carried out by him—and it was soon found to be so convenient as not to make it worth while to abandon it in the later ones.
The keyboard of the colour-organ has therefore been arranged precisely in the same way as that of an organ or a piano; and, as has already been stated, the spectrum-band has been divided up into similar intervals.
This division of the intervals, or notes, corresponding to those of the musical scale, is not quite as simple as it would first appear to be, because of the fact that the rate of dispersion at one end of the spectrum-band is considerably greater than at the other. At the red end, where the dispersion is greatest, the spaces between the points from which the colour is obtained have to be greater in order to provide for the slower increase in rate of vibration, and at the violet end they are consequently closer together. This, however, is 
To shew normal division of colour scale upon keyboard of colour organ, colour musical methods of execution are employed. The figures in the spaces above the colours give the approximate frequencies of aether vibration in millions of millions per second. The colours cannot be accurately given in pigments, and of course do not correspond more than roughly to those produced by the instrument.
The method of musical notation being adopted as to the treble and bass clefs, time values of notes, etc., the ordinary musical directions such as diminuendo, crescendo, allegro, etc., can, of course, be used, and it becomes relatively easy for the executant to use the ordinary form of colour-organ.
Later on it was found convenient to have an alternative arrangement under which the spectrum-band can be spread over the whole of the five or six octaves of the keyboard. By the use of a pneumatic device, the simple withdrawal of a stop has the effect of doing this. A musical system of notation can still be employed, but when this stop is in use, of course, any direct translation of a musical composition is impossible, and a score written with the intention of using this arrangement of the keyboard would appear to the ordinary musician to be quite chaotic. Its chief advantage is to make extemporization in colour easier, and no more need be said for the present about its other uses.
Leaving the musical method of notation aside, we come to another mode of placing the colour effects under the control of the performer, to which some reference has already been made. It is that of using the three primary colours only, and combining them in various degrees of relative strength upon the screen. Under this arrangement each of the three colours can be projected in varying degrees of strength ranging from full power up to white light. Each colour is under the control of a lever, to which is attached an index showing the executant the strength of the colour he is using. The needle of this index passes along a curved scale, upon which figures or letters can be placed at intervals. Two of the levers are moved by the right and left hands of the executant, and the third by the foot. The whole arrangement places the performer more in the position of the violinist 
Levers of a three-colour instrument used conjointly with keyboard colour-organ.
In using any but the musical method, however, the difficulty of easily expressing the duration of a note has to be overcome, or showing whether it is long or short, or accentuated, and so forth. An example is given below of the method of notation employed.
Each space represents a given note as indicated by its number on the index scale, and the length of the space determines the relative length of the note in the bar. The letters R. Y. and B. are the initials of the primaries.
To make the matter clearer by recapitulation:
When using the keyboard colour-organ, whenever a note is depressed its corresponding colour appears upon the screen, and if a chord is struck, combined colours also make their appearance. It will easily be understood that although the intervals taken along the length of the spectrum-band—to give its division into the octave of tones and semitones—are small, as in the case of the pianoforte or organ, there are spaces of colour between these intervals. The keyboard form of instrument cannot therefore provide quite the whole range of colours which appear in nature, although the combinations which are placed at our command are almost limitless.
There is one point of interest which may be mentioned here. When we are using coloured light instead of pigment, although the effects produced are much more beautiful than those obtainable with pigments, it does not seem so easy to obtain some of the grey tints with which suitable pigments will provide us. Greyness is, however, a relative term. In 
System of Notation for Three-Colour Instrument.
The figures give the required position of the lever for each colour upon its scale, the tint within the space below it indicating approximately the strength of the colour. The length of the space gives duration of the note. Three bars of different time are given.
The lower illustration shows a smaller size of the musical staff in which the depth of the colour is not indicated.
Although the present forms of colour-music instruments have cost me a large amount of time and thought and are the outcome of many modifications and experiments, there is still room for improvement in many respects, and I hope to carry out some of these improvements in the future or to be the means of suggesting them to those who may follow me in the pursuit of the subject.
To shew division of colour scale when the spectrum is extended over the whole length of the key-board of the colour organ by spectrum stop.