CLOUDS. 



635 



sufferers a short time since were blinded by reflected light, and dark 

 spectacles are worn on all Alpine expeditions. The invisible rays, as we 

 have said, dissolve the ice into rivers. 



The atmosphere produces clouds by expansion of vapour, which chills 

 or cools it, and it descends as rain. To prove that expansion cools air is 

 easy by experiment, but if we have no apparatus we must make use of our 

 mouths. In the body the breath is warm, as we can assure ourselves by 

 opening our. mouths wide and breathing upon our hands. But close the 

 mouth and blow the same breath outwards through a very small aperture. 

 It is in a slight degree compressed as it issues from the lips, and expanding 

 again in the atmosphere feels colder. Air compressed into a machine and 

 permitted to escape will form ice. 



Water is present in clouds which assume very fantastic and beautiful 

 forms. We know nothing more enjoyable than to sit watching the masses of 

 cumuli on a fine afternoon. The grand masses built up like the Alps appear 



- 7 1 ?- Cumulus cloud. 



to be actual mountains, and yet we knew they arc but vapour floating in the 

 air, and presently to meet with clouds of an opposite disposition, and produce 

 a thunderstorm with torrents of rain. Those who will devote a few minutes 

 every day to the steady examination of clouds, will not be disappointed. 

 They give us all the grandeur of terrestrial scenery. Mountains, plains, white 

 " fleecy seas," upon which tiny cloudlets float, and low upon the imaginary yet 

 apparent horizon, rise other clouds and mimic mountains far and farther 

 away in never-ending distance. 



A pretty, light, feathery cloud, with curling tips and fibres, is known 

 as cirrus, and exists at a very great elevation. Gay-Lussac went up in a 

 balloon 23,000 feet, and even at that height the cirri was far above him in 

 space. We can readily understand that at such an extreme elevation they 

 must be very cold, and they are supposed to consist of tiny particles of ice. 

 Such clouds as these are very frequently observed at night, as cirro-cumulus 

 around the moon, and a yellowish halo, apparent to all observers, is thought 

 to be coloured by the icy particles of the lofty cirrus. The beautiful and 



