If a beam of white light falls upon a white surface, it is reflected without change; but if it falls upon a red surface, only the red ray is reflected: so also with yellow and other colors.

The ray which is reflected corresponds with the color of the object.

It is this reflected decomposed light which prevents the beautifully-colored image we see upon the ground glass in our cameras.
[Illustration: Fig.

2 (amdg_2.gif)] A sunbeam may be capable of three divisions--LIGHT, HEAT, and ACTINISM; the last causes all the chemical changes, and is the acting power upon surfaces prepared to receive the photographic image.

The accompanying illustration, Fig.