648 SCIENTIFIC RECREATIONS. 



If you go under water and look at the sun it will appear very fiery 

 indeed, and we may likewise imagine that fiery crimson rays, which betoken 

 atmospherical disturbance, very often are due to the moisture through which 

 they are transmitted. Wet and storm frequently succeed a crimson sunset, 

 which betokens much moisture in the air. The sun is similarly seen through 

 the steam issuing from an engine, and the colours vary according to the 

 density of the steam in its stages of condensation. 



Vapour, we know, is invisible and transparent, but when it has been 

 condensed into rain-drops, and the sun is shining, if we stand with our backs 

 to the sun we see what we call the rainbow, because a ray of light entering 

 the drop is reflected, and as all rays are not of equal refrangibility, the light, 

 which is composed of three simple rays, is divided and reflected into those and 

 the complementary colours. When the sun is at the horizon, the rainbow, to 



Fig. 729. Mirage at sea. 



an observer on the earth (but not on a mountain), will appear to be a semi- 

 circle. The higher the sun rises the lower is the centre of the rainbow. So 

 we can never see rainbows at noon in summer because the sun is too high. 

 A second rainbow is not uncommon, the second reflection producing the 

 colours in a different order. The colours in the " original " range from violet 

 to red ; in the " copy " they extend from red to violet. " Rainbows " are 

 often visible in the spray of waterfalls and fountains. 



HALOS are frequently observed surrounding the moon, and then we are 

 apt to prognosticate rain. 



" The nearer the wane 

 The farther the rain," 



is an old couplet referring to the appearance of the moon, and is supposed to 

 foreshadow the weather by the size of the halo, which is caused, as we know, 

 by the existence of vesicular vapour in the atmosphere. 



MOCK SUNS, or parhelia, and mock-moons, or paraselenes, are continually 



