The following general method of finding the harmonic colours will enable the reader to determine them for tints not contained in the preceding table. Let =A B=, Fig. 23, be the prismatic spectrum, containing all the seven colours, namely, _Red_, _Orange_, _Yellow_, _Green_, _Blue_, _Indigo_, and _Violet_, in the proportion assigned to them by Sir Isaac Newton, and marked by the dotted lines. Bisect the =A B= at _m_, so that =A _m_= is equal to =B _m_=, and let it be required to ascertain the colour which harmonizes with the colour in the Indigo space at the point _p_. Take =A _m_=, and set it from _p_ to _o_, and the colour opposite _o_, or an orange-yellow, will be that which harmonizes with the indigo at _p_. If _p_ is between _m_ and =A=, then the distance =A _m_= must be set off from _m_ towards _n_. [Illustration: FIG. 23] In order to show the method of constructing object-boxes on the preceding principles, we shall suppose that the harmonic colours of orange-yellow and indigo are to be employed. Four or five regular figures, such as those already described, must be made out of indigo-coloured glass, some of them being plain, and others twisted. The same number of figures must also be made out of an orange-yellow glass; and some of these may be drawn of less diameter than others, in order that tints of various intensities, but of the same colour, may be obtained. Some of these pieces of spun glass, of an indigo colour, may be intertwisted with fibres of the orange-yellow glass. A few pieces of white flint-glass, or crystal spun in a similar manner, and intertwisted, some with fibres of orange-yellow, and others with fibres of indigo glass, should be added; and when all these are joined to some flat fragments of orange-yellow glass, and indigo-coloured glass, and placed in the object-plate, they will exhibit, when applied to the Kaleidoscope, the most chaste combinations of forms and colours, which will not only delight the eye by the beauty of their outline, but also by the perfect harmony of their tints. By using the thin and highly-coloured films or flakes of decomposed glass, very brilliant and beautiful patterns are produced. These films may be placed either upon a mirror plate or upon black wax, and they may be placed among other objects, or fixed in movable cells. By applying the Kaleidoscope to crystals in the act of formation, shooting out in different directions, symmetrical patterns are instantaneously created. The effect produced by objects of only one colour is perhaps even superior to the combination of two harmonic colours. In constructing object-plates of this kind, various shades of the same colour may be adopted; and when such objects are mixed with pieces of colourless glass, twisted and spun, the most chaste and delicate patterns are produced; and those eyes which suffer pain from the contemplation of various colours, are able to look without uneasiness upon a pattern in which there is only one.