It is not expected that the children in the lowest grades will learn much of the science of color, but it is desirable that the teachers have such knowledge of it that they will not unconsciously convey to the children erroneous impressions which must be unlearned later in life.
Concerning the Solar Spectrum.
More than two hundred years ago Sir Isaac Newton discovered that a triangular glass prism would transform a beam of sunlight into a beautiful band of color. If the prism is held in a beam of sunlight which enters a moderately lighted room, there will appear on the walls, ceiling or floor, here and there, as the glass is moved, beautiful spots in rainbow colors. If the room is darkened by shutters, and only a small beam of light is admitted through a very narrow slit and the prism properly adjusted to receive this beam of light, a beautiful band of variegated colors may be thrown on to a white ceiling or screen, and this effect is called a prismatic solar spectrum. A perfect solar spectrum once seen under favorable conditions in a dark room is a sight never to be forgotten.
The accompanying illustration shows the relative positions of the parts named. A is the beam of light as it enters the room. B is the triangular prism. The dotted lines represent groups of rays extending to the vertical band of colors indicated by the letters V for violet at the top, then blue, green, yellow, orange to red at the bottom.
The explanation of this phenomenon is that the beam of sunlight is composed of a great number of different kinds of rays, which in passing through the prism are refracted or bent from their direct course, and some are bent more than others, the red least of all and the violet most. It is supposed that light is propagated by waves or undulations in an extremely rare substance termed ether which is supposed to occupy all space and transparent bodies. These waves are thought to be similar to sound waves in the air or the ripples on the smooth surface of a pond when a pebble is thrown into it. Because so many of the phenomena of light can be satisfactorily explained by this theory, it has been very generally adopted by the scientists. The amount that rays of light are refracted from a straight line in passing through a prism is in proportion to the number of waves or undulations per second, and in inverse proportion to the length of the waves. The red waves are refracted the least and are the longest, while the violet rays are refracted the most and are the shortest.
Fig.1
Whether this theory of the spectrum formation is absolutely correct or not, the fact is established that the colors found in a prismatic solar spectrum are always the same under the same conditions and the order of their arrangement is never changed. By means of the quality of spectrum colors called the wave length, a given color can always be located in the spectrum, and hence if a spectrum color is selected as a standard it can always be determined by its recorded wave length.