CLOUDS SURMOUNTING MOUNTAINS. 47 



is generally met with. The answer I would give to the question is, 

 However plausible the supposition may be, I desiderate evidence that 

 gravitation can occasion a deposit of moisture suspended in a state 

 of solution in the atmosphere, operating on it otherwise than it 

 does upon the other constituents of the air; and the phenomena 

 seen can be accounted for satisfactorily otherwise. 



All that was done by Mount Shehallien was to cause a deflection of 

 the plummet ; the preponderating attraction was towards the earth's 

 centre. The phenomenon under consideration is not a deflection 

 from the perpendicular, but the appearance of clouds on the moun- 

 tains alone. 



We cannot get rid of the idea that the earth by gravitation exerts 

 an attractive force upon clouds, but they do not fall precipitately upon 

 the earth. Solid matter, so comminuted as to appear as dust, floats in 

 the atmosphere for a length of time, rising even with aerial currents 

 in despite of gravitation ; so is it with the molecules of water in a 

 fog. With regard to invisible vapour, it appears to be subject to the 

 law of gaseous diflfusion, in which, though still held by gravitation 

 within the atmosphere, it is free within the limits of this to go any 

 whither. True, moisture can be withdrawn from the atmosphere, and 

 it is so withdrawn, but this is not attributable to gravitation ; it is 

 attributable to chemical affinity, whatever that may be, and it varies 

 with the composition of the soil and the chemical affinity of its con- 

 stituents for moisture. 



In lack of evidence that the attraction of gravitation exercised by 

 the earth abstracts moisture dissolved in the atmosphere from the 

 air, I see no reason to conclude that by gravitation has moisture been 

 abstracted from the air on the mountain top when there the cloud is 

 formed. 



While I desiderate evidence that gravitation can occasion a deposit 

 of moisture suspended in a state of solution in the atmosphere, 

 operating on it otherwise than it does upon the other constituents of 

 the air, and evidence that the gravitation occasioned by mountains 

 difiors in its nature from the more powerful gravitation exercised by 

 the earth, I see no evidence of their attracting clouds ; and all the 

 phenomena connected with the appearance of clouds surmounting 

 mountains may be accounted for in accordance with the way in which 

 the appearance of clouds surmounting forest has been accounted for, 

 that is by a fall of temperature below that at which the vapour there 

 suspended in the atmosphere could be sustained by it in solution. 



It is in defence of that view that the subject comes under consider* 



