Mrs. B. The lens collects an equal number of rays to a focus, whether you hold the white or the brown paper, there; but the white paper appears more luminous in the focus, because most of the rays, instead of entering into the paper, are reflected by it; and this is the reason that the paper does not readily take fire: whilst, on the contrary, the brown paper, which absorbs more light and heat than it reflects, soon becomes heated and takes fire.
Caroline. This is extremely curious; but why should brown paper, absorb more rays, than white paper?
Mrs. B. I am far from being able to give a satisfactory answer to that question. We can form but mere conjecture on this point; it is supposed that the tendency to absorb, or reflect rays, depends on the arrangement of the minute particles of the body, and that this diversity of arrangement renders some bodies susceptible of reflecting one coloured ray, and absorbing the others; whilst other bodies, have a tendency to reflect all the colours, and others again, to absorb them all.
Emily. And how do you know which colours bodies have a tendency to reflect, or which to absorb?
Mrs. B. Because a body always appears to be of the colour which it reflects; for, as we see only by reflected rays, it can appear of the colour of those rays, only.
Caroline. But we see all bodies of their own natural colour, Mrs. B.; the grass and trees, green; the sky, blue; the flowers of various hues.
Mrs. B. True; but why is the grass green?—because it absorbs all, except the green rays; it is, therefore, these only which the grass and trees reflect to our eyes, and this makes them appear green. The flowers, in the same manner, reflect the various colours of which they appear to us; the rose, the red rays; the violet, the blue; the jonquil, the yellow, &c.
Caroline. But these are the permanent colours of the grass and flowers, whether the sun's rays shine on them or not.
Mrs. B. Whenever you see those colours, the flowers must be illumined by some light; and light, from whatever source it proceeds, is of the same nature; composed of the various coloured rays which paint the grass, the flowers, and every coloured object in nature.
Caroline. But, Mrs. B., the grass is green, and the flowers are coloured, whether in the dark, or exposed to the light?