Some of the object-boxes are filled with iron or brass wires, twisted into various forms, and rendered broader and flatter in some places by hammering. These wires, when intermixed with a few small fragments of coloured glass, produce a very fine effect. Other object-plates have been made with pitch, balsam of tolu, gum lac, and thick transparent paints; and when these substances are laid on with judgment, they form excellent objects for the Kaleidoscope. Lace has been introduced with considerable effect, and also festoons of beads strung upon wire or thread; but pieces of glass, with cut and polished faces, are ill fitted for objects. When the object-box is wide, certain insects may be introduced temporarily, without killing or injuring them, and the crystallization of certain salts from their solution, and other chemical changes, may be curiously exhibited. Hitherto we have supposed all colours to be indiscriminately adopted in the selection of objects; but it will be found from experience, that though the eye is pleased with the combination of various objects, yet it derives this pleasure from the beauty and symmetry of the outline, and not from the union of many different tints. Those who are accustomed to this kind of observation, and who are acquainted with the principles of the harmony of colours, will soon perceive the harshness of the effect which is produced by the predominance of one colour, by the juxtaposition of others, and by the accidental union of a number; and even those who are ignorant of these principles, will acknowledge the superior effect which is obtained by the exclusion of all other colours except those which harmonize with each other. In order to enable any person to find what colours harmonize with each other, I have drawn up the following table, which contains the harmonic colours. Deepest Red, Blue and Green equally mixed. Red, Blue and Green, with most Blue, mixed. Orange Red, Blue mixed with much Indigo. Orange, Blue and Indigo, the Indigo predominating. Orange-Yellow, Indigo unmixed. Yellow, Violet and Indigo nearly in equal portions. Greenish Yellow, Pale Violet. Green, Violet. Greenish Blue, Violet and Red in equal portions. Blue, Orange Red, Red. Indigo, Orange-Yellow. Violet, Green. It appears from the preceding table that _Bluish Green_ harmonizes with _Red_, or, in other words, _Red_ is said to be the _accidental colour_ of _Bluish Green_, and _vice versa_. These colours are also called _complementary colours_, because the one is the complement of the other, or what the other wants of white light; that is, when the two colours are mixed, they will always form white by their combination.[4] [4] See the article _Accidental Colours_, in the EDINBURGH ENCYCLOPÆDIA, vol. i. p. 88.