Each of these rays possesses distinctive characters, both as regards their chemical functions and colors.
Sir Isaac Newton proved that the white light emitted p85 by the sun is not so simple as it appears, but is composed of vivid colors, as shown by his beautiful experiment, the Analysis of Light, which is exemplified by the use of a glass prism. (See fig. 1.)
FIG. 1.
The ray of light A, E, being admitted into a darkened room through a hole A, in the shutter, would fall upon the wall at E. As soon as the prism, B, C, is placed in the path of the sunbeam so as to allow it to fall on one of its angles B, the ray will be refracted, or bent out of its course so as to pass through the prism (as in the line D) and not in the same line, A, E, that it would have done had the prism not been interposed.
Another effect also takes place; the ray of white light is decomposed into its component colors, and if you stand at a short distance from the prism, you will see that these colors are spread out in a triangular form, the base of which is on the wall and the apex at the angle C of the prism. Remove the prism and it is seen that the splendid display of colors upon the wall has disappeared, and a round spot of white light, E, is seen below the place occupied by the spectrum.
The colored image on the wall is called the prismatic or solar spectrum, which, according to Sir Isaac Newton, is composed of seven different colors. The color at the lowest portion of the image is red and the one at the other end is violet, the intermediate parts being occupied by five other colors, and the whole arranged p86 according to the table below, the proportion of each color having been measured by Fraunhofer with the greatest care, with the results placed opposite to each, corresponding with the 360 degrees of a circle, the red ray being the least and the violet the most refracted of this chromatic image.
| Violet | 109 |
| Indigo | 47 |
| Blue | 48 |
| Green | 46 |
| Yellow | 27 |
| Orange | 27 |
| Red | 56 |
| 360 |
The sunbeam, the ray of white light, contains powers within it of which the earlier philosophers had but a faint idea, besides its accompanying heat. There is a principle associated intimately with it, which has the power of decomposing and of determining the decomposition of chemical compounds.
This principle is "Actinism" and is as perfectly distinct in the nature of its properties from light, as light is from the principle of heat, with which it is also closely connected.