Part 85

Caroline. Oh, how melancholy would that be; and how pernicious to the sight, to be constantly viewing bright objects against a black sky. But what is the reason that bodies often change their colour; as leaves, which wither in autumn, or a spot of ink, which produces an iron-mould on linen?

Mrs. B. It arises from some chemical change, which takes place in the arrangement of the component parts; by which they lose their tendency to reflect certain colours, and acquire the power of reflecting others. A withered leaf thus no linger reflects the blue rays; it appears, therefore, yellow, or has a slight tendency to reflect several rays, which produce a dingy brown colour.

An ink spot on linen, at first absorbs all the rays; but, from the action of soap, or of some other agent, it undergoes a chemical change, and the spot partially regains its tendency to reflect colours, but with a preference to reflect the yellow rays, and such is the colour of the iron-mould.

Emily. Bodies, then, far from being of the colour which they appear to possess, are of that colour to which they have the greatest aversion, with which they will not incorporate, but reject, and drive from them.

Mrs. B. It certainly is so; though I scarcely dare venture to advance such an opinion, whilst Caroline is contemplating her beautiful rose.

Caroline. My poor rose! you are not satisfied with depriving it of colour, but even make it have an aversion to it; and I am unable to contradict you.

Emily. Since dark bodies, absorb more solar rays than light ones, the former should sooner be heated if exposed to the sun?

Mrs. B. And they are found, by experience, to be so. Have you never observed a black dress, to be warmer than a white one?

Emily. Yes, and a white one more dazzling: the black is heated by absorbing the rays, the white is dazzling, by reflecting them.

Caroline. And this was the reason that the brown paper was burnt in the focus of the lens, whilst the white paper exhibited the most luminous spot, but did not take fire.

Mrs. B. It was so. It is now full time to conclude our lesson. At our next meeting, I shall give you a description of the eye.

Questions

1. (Pg. 179) What is meant by the refraction of light?

2. (Pg. 179) What is believed to be the cause of refraction?

3. (Pg. 180) How is a ray refracted in passing obliquely from air into water?

4. (Pg. 180) How is this refraction explained in fig. 1, plate 19?

5. (Pg. 180) What is fig. 2 intended to explain?

6. (Pg. 180) What is the rule respecting refraction, by different mediums?

7. (Pg. 181) What is meant by the perpendicular?

8. (Pg. 181) How does fig. 3, plate 19, elucidate the law of refraction?

9. (Pg. 181) What will be the effect on the apparent situation of the flower?

10. (Pg. 181) What effect has refraction upon the apparent depth of a stream of water?

11. (Pg. 182) How does the atmosphere refract the rays of the sun, as represented, fig. 4?

12. (Pg. 182) Why have we the rays of the sun always refracted?

13. (Pg. 182) What length of time is required for light to travel from the sun, to the earth?

14. (Pg. 182) What effect has this upon his apparent place?

15. (Pg. 182) How is the length of the day affected by refraction?

16. (Pg. 183) How are rays refracted, which fall obliquely upon a flat pane of glass, (fig. 5, plate 19?)