CHAPTER V.

BURNING MIRRORS-SINGULAR ILLUSIONS-SCIENCE AN ANSUPERSTITION-THE LIGHT OF TRUTH INVALU

TIDOTE TO

ABLE.

SOME knowledge of optics was possessed in very early times. As the ancients discovered that vision is performed in straight lines, they directed their attention to them, and found that when a ray of light falls obliquely on a bright surface it is reflected, and that the angle of reflection is equal to the angle of incidence.

B

A

A

Let A A in the above figure be a bright surface, B the ray of light falling obliquely on it, and C the reflected ray in this case, it is apparent that the angle

s knowledge

that of designing

various objects, as they

fol a given point;--an art

u the end of the fifteenth

aby ben conversant with eets from the surface of The earliest application of wrth which we are sequainted employed by Archimedes,

use, about two hundred years be

(ra. At the siege of that city by

Roman consul, he employed them to

Davy of the assala *. The method he

the fleet of V.

in all div

A

- on hinges, which,

eted them upon the

• reduced to ashes." We

..n the same way destroy i

is, at the siege of Byzantium.

Jupiter's satellites when that planet is farthest from the earth, that light travels to us in seven minutes. It will therefo the one pole of the earth to the other in the part of a second, or at the rate of 190,00 inconsiderable space of time. So amazing that the earth, moving at the rate of nine second, would take two months to pass thi which a ray of light would dart over in