96 



NATURE FOR ITS OWN SAKE 



With the sun shining after a thunder-storm, 

 and the light striking upon the clouds beyond us, 

 comes one of the most noticeable beauties of the 

 sky, the rainbow. It is caused by the drops of 

 water in the air becoming prisms of light and 

 casting the spectrum colors. A thin sheet of 

 these falling drops is struck obliquely by the 

 sun's rays, and each drop has light entering the 

 upper portion of it, and undergoing two refrac- 

 tions and one reflection. The exact scientific 

 explanation of the arch of light, and how it 

 casts the colors of the spectrum, is foreign to 

 the present purpose. Suffice it to say that 

 the arch is seen only when sunlight strikes 

 falling rain obliquely, and that it shows the 

 colors of the spectrum, beginning with red on 

 the outside. The secondary or upper bow is 

 like the first, only fainter, owing to a double 

 reflection within the drops, and with the colors 

 reversed that is, the violet is on the outside. 

 The bow caused by the moon is much fainter 

 than that caused by the sun, and is not fre- 

 quently seen. It rarely shows distinct colors, 

 and is most commonly seen as a pale gleam of 

 white or yellow light. 



The three-days' storm of rain, common to all 

 temperate climates, is quite a different affair 



