1847.] Progressive Changes of Matter. 87 



Clouds are formed of the watery element contained in the at- 

 mosphere when passing into a cold temperature. When steam 

 passes off from boiling water, if rising into a cold atmosphere at 

 the surface of the water it makes a great display of white cloudy 

 vapor. In the summer season this fact is scarcely perceptible. 

 In hot weather a rail road steam engine passes over the plain 

 without being observed, in severe cold winter w^eather, a trail of 

 white clouds comet like, marks its course for a great distance. It 

 is evident therefore, that clouds are formed in a colder medium 

 than that of the surface of the earth, over which they move. The 

 hurried vapors of the atmosphere seem to pass through two de- 

 grees of condensation before rain drops are formed. When clouds 

 are formed the atmosphere may not be sufficiently saturated with 

 water to produce rain ; they continue sometimes for weeks, 

 and are then dispersed without affording showers. But as 

 the evaporation of water at the surface of the earth is constantly 

 taking place, it follows that condensation will also take place 

 at some period, or else all the water in the seas would be carried 

 into the sky. It is a fact, well known, that a warm volume of air 

 becomes contracted on being cooled, and writers on the natural 

 sciences have compared, not inaptly, a body of air saturated with 

 water, to an ordinary sponge saturated with that element ; the 

 only difference is perhaps, that the water in the sponge retains 

 its original identity, in the air it is vaporous. In sultry weather 

 in the summer season, is the most suitable time to contemplate the 

 formation of clouds and rain. Evaporation at that period is rapid, 

 and the extremes of temperature often occur. 



When the upper atmosphere becomes surcharged with an as- 

 cending watery element, condensation is first discovered by the 

 formation of a cloud. This cloud casts at once a shade, the influ- 

 ence of which is felt even at the earth's surface ; an influence also 

 may be felt in the vicinity of the cloud from the same cause. 

 The cold increases, and the cloud accumulates, the centre of 

 which becomes so cold and dense, that the particles of water, are 

 brought into such proximity as to unite in drops and fall. The 

 cloud still increases and draws into its dark freezing bosom the 

 elements of an abundant shower. Whole regions of atmosphere 

 being so suddenly contracted by cold, that fierce winds arise, and 

 a general commotion of the elements ensues. The cloud is wheel- 

 ed about or floated along by some prevailing wind condensing 

 and scattering the buried vapors that fall within its march. In 

 the phenomena of a storm, we see the same forces that contribut- 

 ed so essentially to its formation, contributing also as essen- 

 tially to its destruction. The shade, the cold, and the winds 

 all combined to exhaust the atmosphere of its watery element 

 to a degree far below what it was capable of bearing in a 



