THE ESSENTIAL COLORS 139 



used in the same way instead of green and violet, the rotating 

 disk will appear yellow. A combination of red and yellow 

 will give orange. The colors formed in this way do not appear 

 to the eye different from the spectrum colors, but they are 

 actually very different. The spectrum colors, as we saw in 

 the preceding Section, are pure, simple colors, while the colors 

 formed from the rotating disk are in reality compounded of 

 several totally different rays, although in appearance the 

 resulting colors are pure and simple. 



If it were not that colors can be compounded, we should 

 be limited in hue and shade to the seven spectral colors ; the 

 wealth and beauty of color in nature, art, and commerce would 

 be unknown ; the flowers with their thousands of hues would 

 have a poverty of color undreamed of; art would lose its 

 magenta, its lilac, its olive, its lavender, and would have to 

 work its wonders with the spectral colors alone. By com- 

 pounding various colors in different proportions, new colors 

 can be formed to give freshness and variety. If one third of 

 the rotating disk is painted blue, and the remainder white, the 

 result is lavender ; if fifteen parts of white, four parts of red, 

 and one part of blue are arranged on the disk, the result is 

 lilac. Olive is obtained from a combination of two parts green, 

 one part red, and one part black ; and the soft rich shades of 

 brown are all due to different mixtures of black, red, orange, 

 or yellow. 



134. The Essential Colors. Strange and unexpected facts 

 await us at every turn in science ! If the rotating cardboard 

 disk (Fig. 88) is painted one third red, one third green, and 

 one third blue, the resulting color is white. While the mix- 

 ture of the seven spectral colors produces white, it is not 

 necessary to have all of those seven colors in order to obtain 

 white ; because a mixture of the following colors alone, red, 

 green, and blue, will give white. Moreover, by the mixture of 



