476 RUM. PARASITIC CLOUDS. 



less it retired in the direction of the current of air, 

 diminishing in density as it receded from the mountain ; 

 and having reached a distance equal to that at which 

 it first began to form, it suddenly dissolved and disap- 

 peared, its place being uninterruptedly supplied by a fresh 

 formation. 



The cloud which rested beneath the summit of the other 

 mountain, seemed for a considerable time in a state of 

 absolute tranquillity, undergoing no sudden changes of 

 shape, but forming a dark stratum. It was soon however 

 obvious that this also was in a similar state of constant 

 renovation and waste, although its changes of figure were 

 much less apparent ; and that this mountain, like its 

 neighbour, was causing a perpetual precipitation of fresh 

 vapour from the atmosphere as far as its influence 

 extended ; that vapour being again dissolved in the air 

 as the current drove it from the sphere of the mountain's 

 action. 



It is plain that if the solution of the vapour in the 

 atmosphere had not kept pace with its precipitation by 

 these two mountains, the whole visible sky would soon 

 have been covered with clouds ; so small a surface of land 

 in a particular condition having the power of producing 

 such a constant and large precipitation of vapour. It 

 would not have required an hour to have involved the 

 whole surrounding country in clouds and darkness. That 

 this effect did not take place was probably owing to the 

 direction of the wind, which blew from the land to the 

 sea. Had it blown in the opposite direction, it is pro- 

 bable that the constant action of fresh portions of land 

 would have continued the effect at first produced. It is 

 unnecessary to point out the coincidence of this pheno- 

 menon with the well known power of land in generating 

 clouds from those currents of air which blow from sea ; 

 nor with the equally well known property of high moun- 

 tains in determining the formation of clouds and the 

 fall of rain on certain tracts of country. In this particular 



