of the fall of Bain as the height increases. 11 



169 feet, a result with which it seems impossible to reconcile 

 the condensation hypothesis, except by supposing the hygro- 

 metric condition of the atmosphere to vary with the height 

 above the ground, in some abrupt and unaccountable manner 

 not hitherto observed. 



But though these difficulties attend the hypothesis of Dr 

 Franklin and Professor Phillips, it is to be remarked that 

 they have no reference to the nature of the cause which it 

 assigns, but simply to the degree of its efficacy. For, while it 

 scarcely admits of a doubt that there is a condensation of 

 vapour on the cold surface of each rain drop, and that thereby 

 the rain is augmented in its progress downwards ; on the other 

 hand, the observed rate of augmentation is such, that it cannot 

 be accounted for, without supposing the co-operation of some 

 other cause. 



The object of the few following remarks is to suggest, as a 

 supplement to the foregoing hypothesis, an additional cause 

 of the increase of the rain as it approaches the ground. This 

 supplementary hypothesis is as follows. 



From the inequality of the marks which the first drops of a 

 shower of rain make upon any smooth surface, it is inferred 

 that the drops themselves are of unequal size. But independ- 

 ently of direct proof, it seems very unlikely that, in the original 

 formation of rain, each drop should be exactly of the same 

 size ; and, allowing the possibility of such an equality, it is 

 still more unlikely that it should continue for an instant, since 

 the slightest disturbance of their descending motion would 

 cause many of the drops to coalesce. 



It is assumed, therefore, that even at the elevation where 

 the rain is formed, the drops in the same horizontal stratum 

 are not of the same size. If there were no air, each drop in 

 such a stratum would reach the ground at the same moment ; 

 but since in reality the spherules of rain are resisted by the 

 air, it follows, from well-known mechanical principles, that 

 the larger drops will outstrip, in their descent, the smaller 

 ones in the same stratum, and will overtake those in the next 

 lower stratum. But in penetrating this stratum, they will 

 necessarily carry before them and coalesce with the drops 



