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Charles. And was that the cause of the colours which we saw on some soap bubbles which James was making with a tobacco-pipe ?

Tutor. It was.


Of Colours.

CHARLES. After what you said yesterday, I am at a loss to know the cause of different colours ; the cloth on this table is green ; that of which my coat is made is blue, whạt makes the difference in these? Am I to believe the poet, that

Colours are but phantoms of the day,
With that they're born, with that they fade away;
Like beauty's charms, they but amuse the sight,
Dark in themselves, till by reflection bright;
With the sun's aid to rival him they boast,
But light withdraw, in their own shades are lost.


Tutor. All colours are supposed to exist only in the light of luminous bodies, such as the sun, a candle, &c. and that light falling incessantly upon different bodies is separated into its seven primitive colours, some of which are absorbed, while others are refected. James. Is it from the reflected

rays that we judge of the colour of objects ?

Tutor. It has generally been thought so ; thus the cloth on the table absorbs all the rays but the

green, which it reflects to the eye ; but your

coat is of a different texture, and absorbs all but the blue

rays. Charles. Why is paper and the show white? Tutor. T'he whiteness of


is occasioned by its reflecting the greatest part of all the rays that fall upon it. And every Aake of snow being an assemblage of frozen globules of water sticking together, reflects and refracts the light that falls upon it in all directions so as to mix it very intimately, and produce a white image on the eye.

James. Does the whiteness of the sun's

light arise from a mixture of all the primary colours?

Tutor. It does, as may be easily proved by an experiment, for if any of the seven colours be intercepted at the lens, the image in a great measure loses its whiteness. With the prism I will divide the ray into its seven colours,* I will then take a convex lens in order to re-unite them into a single raya which will exhibit a round image of a shining white; but if only five or six of these rays be taken with the lens, it will produce a dusky white.

Charles. And yet to this white colour of the sun we are indebted for all the fine colours exhibited in nature :

Fairest of beings ! first created light!
Prime cause of beauty! for from thee alone,
The sparkling gem, the vegetable race,
The nobler worlds that live and breathe, their charms,
The lovely hues peculiar to each tribe,
From thy unfailing source of splendour draw.


A figure will be given on this subject with explanations, Conversation XVIII. on the Rainbow.

Tutor. These are very appropriate lines, for without light the diamond would lose all its beauty

James. The diamond, I know, owes its brilliancy to the power of reflecting almost all the


of light that fall on it: but are vegetable and animal tribes equally indebted to it?

Tutor. What does the gardener do to make his endive and lettuces white ?

Charles. He ties them up.

Tutor. That is, he shuts out the light, and by this means they become blanched. I could produce you a thousand instances to show, not only that the colour, but even the existence of vegetables, depend upon light. Close wooded trees have only leaves on the outside, such is the cedar in the garden. Look up the inside of a yew tree, and you will see that the inner branches are almost, or altogether barren of leaves.. Geraniums and other green-house plants turn their flowers to the light; and plants in general, if doomed to darkness, soon sicken and die.

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