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
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