orange 27; yellow 40; green 60; blue 60; indigo 48; violet 80; or 360 in all. Or it may be seen still better, by painting the rim of a wheel with the seven colours, and making it turn very rapidly about its axis. In both cases the mixture of the colours will be a sort of greyish white; perfect accuracy, which, however, is not to be attained, would make it a pure white. The coloured rays, separated by a prism, and made to fall

on a glass which will bring them to a focus, causes them to appear white.

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This effect may also be shown by an instrument which the cut represents. It is a disc, on equal divisions of which are painted the seven colours, and these being made to revolve on an axis with great rapidity, the disc appears almost colourless. Were a perfect arrangement made of the various hues, and also proportionate 'velocity given to the disc, no tint whatever would be discoverable.

In variety of colour, as well as in every other instance of Divine operation, we discover an end worthy the Infinite Creator, who "has made nothing in vain," and who "doeth all things well." And let us remember, that our duty and privilege are most graciously combined; for it is recorded by the inspired psalmist, "The works of the Lord are great, sought out of all them that have pleasure therein.-He hath made his wonderful works to be remembered: the Lord is gracious and full of compassion." Psalm cxi. 2-4. "Whoso is wise, and will observe these things, even they shall understand the loving-kindness of the Lord." Psalm cvii. 43.

CHAPTER VIII.

COLOURS OF BODIES-REMARKABLE ACCIDENT.

OTHER facts remain to be noticed, in reference to colour. If, for example, a piece of brown paper be held in the focus of a burning glass, it will take fire almost immediately, much sooner, indeed, than white paper, though it would appear more bright, because most of the rays, instead of entering into the paper, are reflected by it; whilst, on the contrary, the brown paper, which absorbs more light than it reflects, soon becomes heated and takes fire.

The reason of its doing so cannot be satisfactorily explained; but it is supposed that the particles of bodies are variously arranged, so that some reflect one coloured ray, and absorb the rest, whilst others reflect all the colours, and some absorb all.

A body always appears to be of the colour which it reflects; for, as we see only by reflected rays, it can only be of the colour they have. A violet reflects the

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Scarlet

violet rays alone, and absorbs the others. cloth absorbs almost all the colours, except red. Yellow cloth reflects the yellow rays most abundantly, and blue cloth those that are blue. Thus colour appears to be not a property of matter, but the result of matter acting on light. A white ribbon reflects all the rays, but when dyed red, the particles of the silk acquire the property of reflecting the red rays most abundantly, and of absorbing the others.

The dependence of colours on light may be shown in an interesting manner. Let a ray of light be admitted into a darkened room, and then refracted by a prism; if a rose be afterwards exposed to the red rays, the flower will appear more brilliant, but the leaves will be of a dingy brown with a reddish glow, receiving this tinge from the reflection of a few of the red rays, which blend with their natural blackness. If, afterwards, the rose be held in the blue rays, it will no longer be red, but of a dingy blue colour; while, as the leaves reflect both blue and yellow rays, which produce a green colour, and as they have a tendency to reflect the coloured ray in which they are placed, they will reflect more of the blue rays than the rose, and will appear of a brighter blue.

The colours of transparent bodies depend on the

H

property of unequal absorption; for they receive their colour from their power of stopping or absorbing some of the colours of white light and transmitting others. The rich dark light transmitted by a small blue glass is not one colour, like the blue or indigo exhibited by the prism, but a mixture of all the colours of white light, which the glass has not absorbed. These are such as, mixed with the blue tint, would form white light.

When light is reflected from the surfaces of transparent bodies, or transmitted through portions of them with parallel surfaces, it is always white. The thinnest films of blown glass, or those of mica generally met with, will both reflect and transmit white light. If, however, their thickness be diminished to a certain degree, the light is in both cases coloured.

Could a film of mica be produced, with only one tenth part of the thickness of that which produces a bright blue colour, it would reflect no light, and would appear black, if viewed by reflection against a black body. Such a film is not likely to be made, yet accident, on one occasion, produced solid fibres as thin, and actually incapable of reflecting light. A crystal of quartz, of a smoky colour, being broken in two, the two surfaces of fracture were absolutely black, and this appeared at first to arise from a thin opaque film. But