HALO AND PARHELIA. 77 



As fresh in yon horizon dark^ 



As young thy beauties seem, 

 As when the eagle from the ark 



First sported in thy beam. 



For faithful to its sacred page, 



Heaven still rebuilds thy span, 

 Nor lets the type grow pale with age, 



That first spoke peace to man. 



Campbell. 



In serene weather, we often observe a circular light, or 

 luminous ring surrounding the moon ; it is called a halo, 

 or crown. Its outline sometimes faintly shows the colours 

 of the rainbow. The moon is in the middle of this ring, 

 and the intermediate space is generally darker than the rest 

 of the sky. When the moon is at the full, and consider- 

 ably elevated above the horizon, the ring appears most lu- 

 minous. It is often very large. We are not right in sup- 

 posing, that this circle really surrounds the moon ; the true 

 cause of such an appearance must be looked for in our at- 

 mosphere, the vapours of which make a refraction of the 

 rays of light. False moons are sometimes seen near the real 

 moon, and appear as large, but their light is paler. They 

 are generally accompanied by circles, some of which have 

 the same colours as the rainbow, whilst others are white, 

 and others have long luminous tails. All these appearances 

 are produced by refraction. The rays of light falling from 

 the moon upon aqueous and sometimes frozen vapours, are 

 refracted in various ways ; the coloured rays are separated, 

 and reaching the eye present a new image of the moon. 



Parhelia or mock-suns are far more rarely seen, but their 

 appearance is wonderfully curious. They generally appear 

 about the size of the true sun, not quite so bright, though they 

 are said sometimes to rival their parent luminary in splen- 

 dour. When there are a number of them they are not equal 

 to each other in brightness. Externally, they are tinged 

 with colours like the rainbow. They are not always round, 

 and have sometimes a long fiery tail opposite the sun, but 

 are paler towards the extremity. They are formed by the 

 reflection of the sun's beams on a cloud. 



Questions. — 1. Under what circumstances do we perceive the 

 rainbow ? 2. What ie a halo ? 3 What are parhelia, or raock-8U»s 

 7» 



