Fring'd lovely; splendid those in liquid gold: And speak their sovereign's state. He comes, behold!

Fountain of light and colour, warmth and life! The king of glory!

MALLET.

T

Charles. Are we to understand that all colours depend on the reflection of the several coloured rays of light?

Tutor. This seems to have been the opinion of Sir Isaac Newton; but he concluded from various experiments on this subject, that every substance in nature, provided it be reduced to a proper degree of thinness, is transparent. Many transparent media reflect one colour, and transmit another: gold-leaf reflects the yellow, but it transmits a sort of

green

colour by holding it up against a strong light.

Mr. Delaval, a gentleman who a few years since made many experiments to ascertain how colours are produced, undertakes to show that they are exhibited by transmitted light alone, and not by reflected light.

- James. I do not see how that can be the case with bodies that are not transparent.

Tutor He infers, from his experiments, which you may hereafter examine for yourselves, that the original fibres of all substances, when cleared of heterogeneous matter, are perfectly white, and that the rays of light are reflected from these white particles through the colouring matter with which they are covered, and

that this colouring matter serves to

rays

intercept certain in their passage through it, while a free passage being left to others, they will exhibit, according to these circumstances, different colours.-The red colour of the shells of lobsters after boiling, he says, is only a superficial covering spread over the white calcareous earth, of which the shells are composed, and may be removed by scraping or filing. Before the application of heat it is so thick as to appear black, being too thick to admit the passage of light to the shell and back again. The case is the same with feathers, which owe their colours to a thin layer of transparent matter on a white ground.

CONVERSATION X.

Reflected Light, and Plain Mirrors.

TUTOR. We now come to treat of a different species of glasses, viz. of mirrors, or, as they are sometimes called, specula.

James. A looking-glass is a mirror, is it not?

Tutor. Mirrors are made of glass, silvered on one side; they are also made of highly polished metal. There are three kinds of mirrors, the plain, the conver, and the concave.

Charles. You have shown us that in a looking-glass or plain mirror, "The angle of reflection is always "equal to the angle of incidence* "

Tutor. This rule is not only applicable to plain mirrors, but to those which are convex and concave also, as I shall show you to-morrow. But I wish to make some observations first on plain mirrors. In the first place, if you wish to see the complete image of yourself in a plain mirror or looking-glass, it must be half as long as you are high.

James. I should have imagined the glass must have been as long as I am high.

Tutor. In looking at your image in the glass, does it not seem to be as

* See p. 18..