colour composition may be either warm or cool in tendency, or with strong or merely delicate transitions and variations. It may also, for instance, be written in a general key of some one particular colour which is predominant throughout, and in which contrast is very sparingly used, or it may be greatly broken up and with rapid alternations of contrast.
Contrast is more demanded at first and less later on, and there are many other points of this kind which are of interest, but into which it would be tedious to enter at any length in the absence of actual demonstration.
One of the difficulties with which mobile colour has had to deal is that of wide fluctuations of luminosity in the compound tints, and various mechanical devices have been designed and experimented with in the construction of the instrument in order to overcome this. To a large extent it has been now avoided, and it has been found that extreme and disagreeable alternations in luminosity are chiefly due to ineptitude in composition or extemporization.
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