Many of the experiments of the color wheel can be produced with a small toy called a Color Top, which is shown in Fig. 4. It is composed of a thick cardboard disk forming the body of in the operation of the Color Wheel the top and a central wooden spindle on which the disk closely fits. A number of colored paper disks are provided with this top so that very many of the experiments performed before a class can be repeated individually by the pupils and in this way the facts which may have been demonstrated to the class with the color wheel can be fixed in the minds of the pupils by their own experiments with the top. Also as a home toy in the hands of the pupils it can be of value, not only to the children, but to the parents as well.
Use of the Disks.
Fig. 5 shows the method of joining two Maxwell disks and Fig. 6 their appearance when properly joined to be placed on the rotating spindle of the color wheel. In joining two or more disks for use on a color wheel or top, care should be taken to place them in such relation to each other that when rotated the radial edges exposed on the face toward the audience will not "catch the wind." With small disks on the color wheel this is not important, and if there is no whole graduated disk on the arbor behind the slitted disks there is no advantage, but in using the larger disks it is well to put the graduated disk behind the others for this purpose, as at best it is quite laborious to keep up speed when using several of the large disks, even with the best possible conditions. With the thin paper disks of the color in the operation of the Color Wheel top this is an important matter. It will be noticed that the method of joining the disks for use on the Color Top is the reverse of that to be observed with the disks of the Color Wheel as shown in Fig. 5.
| Fig. 5. | Fig. 6. | Fig. 7. |
Fig. 7 shows the same two color disks placed in front of a large white disk having its edge graduated to one hundred parts, so that the relative proportions of two or more colors to be combined can be determined accurately.
As the smaller disks offer so much less resistance in rotation than the larger ones they are most desirable in private experiments or before a small class, and the largest disks of the Normal School Wheel are necessary only when more than three expressions of color are required to be shown at the same time. In making experiments before an audience those persons in front should if possible be at least ten feet from the color wheel. From ten to forty feet there seems to be but little difference in the color perception, but for best tests fifteen to twenty feet is the most desirable position.
For private practice with the color wheel a small mirror may be placed five or six feet in front of the wheel in such position as to furnish an image of the disks to the person operating the machine. Owing to a slight loss of light by reflection the closest criticism may not be possible when working with a mirror in this way, but if a plate mirror is used the results are very good and a bevel plate mirror about 7 x 9 inches without frame, can usually be procured at small cost; this method is much more satisfactory for personal experimenting than an assistant to turn the wheel.
These disks have heretofore been used as a curious piece of philosophical apparatus rather than because they have been supposed to have any practical value in color training, but in establishing a color nomenclature based on six spectrum colors the disks at once assume a great value and are indispensable in a system of color instruction founded on the science of color and on the psychological perception of colors.
Let us suppose that the two disks shown in Fig. 7 are yellow and green, 80 parts yellow and 20 parts green; then by rotation we shall have a green yellow indicated by the symbol Y. 80, G. 20. No argument is necessary to prove that when an exact expression of color effect is required this is better than the simple statement that it is a greenish yellow.