The Glass Prism.
A glass prism is one of the first requisites in the appliances for teaching color, and a prism which may be bought for a few cents will work wonders in the hands of an interested teacher, although a more perfect instrument, such as is sold with physical apparatus, will give colors which are better defined.
Experience in many schoolrooms has proved that a spectrum can be shown somewhere in the average room at some hour in every sunny day, especially in the longer days of spring and summer, and it is well to have the prism when not in use so fixed as to project the spectrum into the room much of the time, so that it may become familiar to the younger children.
Observation of the spectrum enthuses the children with a feeling for color which can be developed in no other way, and they never tire with watching the wonderful vibrating effects of the liquid colors; and by studying it the mental image of each of the six colors becomes as distinct as that of the cube after it has been handled and modeled. If the schoolroom is provided with shutters or dark curtains a much better spectrum can be produced by closing them, as even a slight change from a bright sunny daylight has a very perceptible effect in bringing out the colors. A person who has never seen a carefully prepared spectrum in a room almost perfectly dark can have no realizing sense of the purest possible expressions of color.
Accident once disclosed a simple means by which one teacher secured a very good spectrum. There was a deep, dark closet opening from the schoolroom and one bright day when the prism was being used the spectrum was accidentally thrown into this closet, and the sudden and enthusiastic expression of approval by those pupils who were in position to discover it was certainly interesting to the teacher of that country school, with a dark coal closet.
In a spectrum such as can be produced in a dark room with the most perfect form of prism, all the various colors can be separated and carefully examined and by special appliances compared with pigmentary colors. Experiments of this kind are exceedingly interesting and instructive, and demonstrate the wonderful intensity and purity of the spectrum colors as compared with the purest pigmentary colors that can be produced. Such experiments were carried to a great degree of perfection when the six standard colors for the Bradley Colored Papers were selected.