COLOR AND CHEMICAL ACTION OF LIGHT 381 



colors. Prussian blue reflects blue, green and violet light waves. 

 In white light it looks Prussian blue; in green light the material 

 covered with Prussian blue looks green; in violet light, violet. The 

 colors violet and green are not very strong, as not much of this 

 color is reflected. 



The color of an object, then, depends upon what light waves 

 it reflects or absorbs. Color is a sensation, and not an object. 



FIG. 264. Color depends upon the light rays reflected. When red, green and 

 blue rays are reflected by any object, the object appears white (Figure on 

 top, left row). When red and green rays are reflected and blue is absorbed 

 the object will look yellow. (Central figure, top line.) What is the 

 effect if red and blue are reflected and green is absorbed? What causes 

 a substance to look blue? (First figure left, second row.) What causes 

 a book to appear green? When will cloth look red? When will paper 

 look black? What color rays is a white rose reflecting? What color 

 will a white rose look if viewed through a red glass? Why? What color 

 ray is a red rose reflecting? What happens to the other two rays? Why 

 does everything look blue through a blue glass? Why do things look black 

 through a red and a blue glass? What happens when red objects are 

 viewed through blue glasses? 



Color Blindness. Sometimes one of the sets of color nerves is 

 lacking or much weakened in a person. This causes a yellow object 

 to appear green to a person lacking the red nerve set, since yellow 

 is a combined effect produced by the stimulation of red and green 

 nerves. Engineers of a railroad must be tested to be sure that 

 they do not lack the red set of nerves, since red is the danger signal. 

 Color blindness may be the cause of many people wearing a com- 

 bination of colors which is not pleasing. Men, as a rule, are affected 

 more than women with color blindness. 



Color Printing. Many colors are produced to-day by mixing colors 

 in impressions. The colors used are yellow, red and blue. Some- 

 times black is also employed. Many of our colored pictures are 

 produced by this process. 



Chemical Action of Light. The chemical action of light is used 

 in photography. The light rays reflected from the image are caught 

 by a lens in a camera, and an image is produced on sensitive plates 

 or films. Developing produces on these an image called a negative, 

 from which positives or photographs may be obtained. 



