438 



Marvels of the Universe 



bright rings of liglit encircling the sun or moon at a radius of about twentj'-two degrees. These are 

 called halos, and are caused by the ice-crj^stals refracting the sun's rays. Hales are popularly 

 regarded as portents of coming storm or wet weather, owing to the fact that large quantities of 

 Cirro-stratus are usually found in the front of an approaching atmospheric depression. 



Next in order of height come the Cirro-cumulus and Alto-cumulus types, and as a rule they accom- 

 pany fine weather. The general characteristics of these two types are similar ; but while the Cirro- 

 cumulus may be as high as twenty-three thousand feet, the Alto-cumulus may be found as low as 

 ten thousand feet. These clouds are extremely beautiful when stretched across the sky in long 

 bands and fleecy masses, exhibiting a wav}', rippled structure, or marshalled in parallel lines of tiny 

 cloudlets, and the fancied resemblance of the ripples to the markings on a mackerel has earned for 



[(?. A. aarie. 



LENTICULAR FORM OF ALTO-CUMULUS. 



This again is a form of cloud much in evidence during fine sunsets. The edges of the cloud reflect Intense colours, \vhich 

 form a fine contrast with their denser parts and produce those wonderful effects that are so fascinating to the beholder. 



them the name of " mackerel sky." One particular form of these clouds — the lenticular one — 

 gives rise to our most beautiful sunsets ; for, when the last rays of the sun impinge upon their 

 rippled under-surfaces, the whole sky seems transformed into a sea of shining gold or fiery crimson. 



Still lower down, at about six thousand five hundred feet, is found a similar but much heavier 

 cloud, called Strata-cumulus. This is a type frequently to be seen, and is sometimes heavy enough 

 to cover the whole sky with its dark, wavy masses. 



About the ten thousand feet level there is occasionally seen a uniform, greyish sheet called 

 Alto-stratus, through which the sun shines dimly. It is the " watery sky " of popular weather-lore, 

 and is almost always followed by rain. Owing to its uniformity it cannot be photographed 

 effectively. 



The Cumulus, or " wool-pack " clouds, are probably the best known of all clouds, and consist of 



