96 
NATURE FOR ITS OWN SAKE 
The rain- 
bow, 
bow. 
With the sun shining after a thunder-storm, 
and the light striking upon the clouds beyond us, 
comes one of the most noticeable beanties 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 cansed 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 
