106 



HOW WE LIGHT OUR HOMES 



learned that light is a wave motion in the ether. How- 

 ever, sunlight does not 

 consist of waves of just 

 one wave length but a 

 mixture of waves of 

 different wave lengths. 

 Each wave length pro- 

 duces its own charac- 

 teristic color while all 

 of them together pro- 

 duce white light. This 

 can be shown to be 

 true by passing a ray 

 of sunlight through a 

 glass prism (see Fig. 

 161) which spreads the 

 light so that all the col- 

 ors show. The set of 



color bands produced by the prism is called a spectrum. 

 There are seven spectrum colors and they always ap- 

 pear in the following order: red, orange, yellow, 

 green, blue, indigo, and violet. 



Light waves are extremely short waves, especially 

 in comparison with the length of sound waves. The 

 following table gives the approximate wave lengths 

 in centimeters for six colors. 



FIG. 160. LIGHT THROUGH PLATE 



GLASS 



ABCD PERPENDICULAR RAY 

 abed SLANTING RAY 



WAVE LENGTHS OF LIGHT 



Red 0.000068 cm. Green 



Orange 0.000063 cm. Blue 



Yellow 0.000059 cm. Violet . 



.0.000052 cm. 

 .0.000046 cm. 

 .0.000040 cm. 



The color of an object, when sunlight illuminates 

 it, depends upon the wave lengths which the object 

 reflects or transmits. A piece of white paper is white 

 because it reflects all wave lengths of the spectrum 

 equally. An object is red if it reflects only the wave 

 length that produces red while the other waves of the 

 spectrum are absorbed. An object that absorbs all 



FIG. 161. BREAKING UP OF SUNLIGHT BY A PRISM 



the light waves of the spectrum appears black ; black- 

 ness really means a total absence of color. 



Objects looked at under artificial light do not show 

 their true colors because artificial light is generally 

 deficient in some of the spectrum colors. It is always 

 safer to select goods and clothing under natural light. 



The rainbow is one of our most common displays of 

 the spectrum. It is usually seen early in the morning 

 or late in the afternoon when the sun's rays come 



through the clouds while rain is still falling. If a 

 rainbow occurs in the morning it is usually seen in the 

 west while an afternoon rainbow shines forth in the 

 east. One must have his back to the- sun to see a 

 rainbow. 



As the rays of sunlight enter raindrops, the light 

 is bent and reflected. Thus the white light is broken 

 up into its various wave lengths as it was by the 

 prism. Each raindrop sends out the whole range of 

 spectrum colors from red to violet, but at different 

 angles. Therefore, a drop high up above the earth may 

 send only red rays direct to the eye while the others 

 at different angles pass by. In the same manner a drop 

 of water at a lower altitude may be at the correct 

 angle to send only the violet waves directly to the 

 eye, all other waves passing by. Between these drops 

 others furnish the orange, green, and blue waves so 

 that the eye sees a continuous color band or spectrum 

 across the sky. Figure 162 shows how a raindrop 

 breaks the light ray into its wave lengths. 



If sunlight strikes raindrops at still higher altitudes, 

 the light may be twice reflected and refracted inside 

 the drop and thus cause a second rainbow above the 

 other one. Figure 163 shows how this happens and 

 why the spectrum colors are reversed in order in this 

 second bow. 



White 



-Violet 

 "Red 



FIG. 162. DROP OF WATER WITH 

 SINGLE REFLECTION 



FIG. 163. DOUBLE REFLECTION 

 INSIDE A RAINDROP 



What are some other ether waves? The human eye 

 is able to see only a comparatively short range of 

 wave lengths, but beyond each end of the spectrum 

 there are longer and shorter ether waves that do not 

 affect the optic nerve of the human eye. Beyond vi- 

 olet, the shortest wave of the spectrum, are the in- 

 visible ultra-violet rays that are given off in great 

 quantity by the sun. We mentioned in the study of 

 foods that these rays exert a beneficial influence upon 

 living things and produce the same effect in the hu- 

 man body as vitamin D. 



They are also responsible to a large extent for the 

 chemical action that takes place on a photographic 

 film ; this is the reason we get our best snapshots 

 between about nine in the morning and four in the 

 afternoon. Ultra-violet rays also produce sunburn, 



