Principles on which Clouds arc suspended, 249 



And yet, the more we contemplate the works of nature, the 

 more we are impressed with our own insignificance, and the 

 greatness of the Almighty Creator ; and the longer we live, 

 the more we shall find we have to learn; for 



" 'Tis but a part we see, and not the whole." 



In order to ascertain the principle of the suspension of 

 clouds, particular attention will be necessary both to the tem- 

 perature and density of the atmosphere, as the quantity of 

 moisture it is capable of dissolving greatly depends upon these 

 circumstances. A much larger portion of aqueous vapour, 

 it must be recollected, is held in an elastic form near the 

 surface of the earth, than in the more elevated regions of the 

 clouds. In high regions, even on the summits of high moun- 

 tains, atmospheric pressure opposes very little check to the 

 natural tendency of water to assume an aeriform state; con- 

 sequently, the higher we ascend in the atmosphere, the quantity 

 of moisture which is held in solution goes on diminishing, 

 until we arrive at the precise altitude beyond which the effect 

 of diminished pressure predominates, and the aqueous vapour 

 goes on increasing, according to Professor Leslie's Relations 

 of Heat and Moisture, This is, then, that medium point in 

 the atmosphere which clouds occupy, and above which they 

 rarely ascend, at least so far as my observations go ; and I am 

 led to this conclusion by that beautiful provision made by 

 nature for preserving a constant circulation in the atmo- 

 sphere by causing every accession of heat to be invariably 

 accompanied by a corresponding decrease in density. Sup- 

 posing, then, an ascending column of air to have reached that 

 particular height at which its diminished temperature no longer 

 allows of its retaining the whole quantity of moisture it had 

 dissolved near the surface of the earth : it follows, that a por- 

 tion of water becomes disengaged in that state which is termed 

 by meteorologists vesicular vapour ; that is, as I understand 

 it, vapour holding intermixed with it some portion of atmo- 

 spheric air ; hence it appears, that, as the air is considerably 

 more rare about the usual elevation of the clouds (from two 

 to three miles), it not unfrequently occurs, that the watery 

 globules in their descent meet with a stratum of air of that 

 density which is just equivalent to the weight of the vesicular 

 vapour and the contained atmospheric air together. At 

 this point they will remain suspended, till such time as the air 

 contained within the different vesicles becomes of equal density 

 with the surrounding atmosphere ; when the particles will 

 coalesce, and form larger drops, and, consequently, become 

 -too heavy for the atmosphere to support; and, hence, they 



