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REFLECTION OF LIGHT.

It is well known that if a portion of a beam of light be inter-cepted by any body, the shadow of that body will be boundedby right lines, passing from the luminous body, and meetingthe lines which terminate the opaque body.

Experiment I.

Darken a room into which the sun shines and only admit thelight by a small hole in the window shutter; and place oppositeto the hole a board or screen. If we look at the screen we ob-serve thereon, a picture of all the exterior objects which are op-posite to the hole in all their natural colours: these coloursare faintly depicted; the images of the objects that are stationary,as houses, trees, &c. are likewise fixed or stationary in the pic-ture; whilst the images of those that are in motion, as those ofhorses, carriages, &c. are seen to move. If we place our eye,in this ray, we find that our eye, the light and the hole, are inone and the same straight line. Which is a clear proof that lightis emitted in straight lines, by the luminous bodies

It is equally obvious from light finding no passage throughbent or crooked tubes.

4. REFLECTION OF LIGHT.

Another property of the rays of light is their reflexilility ordisposition of being turned back into the medium in which theymoved with a certain obliquity, so that the light is driven back,without coming into contact with die matter which repels it.

The ray is dien said to be reflected. The angle of reflection isalways equal to the angle of incidence.

When a ray of light falls upon a polished medium, for instancea plate of glass or mirror with a certain obliquity, it does notenter the glass at all, but is reflected when it approaches its sur-face. When a ray of light enters other transparent media it con-