92 



NATURE FOR ITS OWN SAKE 



clens, so to speak, and that by augmented con- 

 densation the spherule gradually grows to a 

 rain-drop. Once formed, the drop has about 

 it an elastic skin or envelope that prevents it 

 from breaking unless pressed or struck by some 

 body. Oftentimes it preserves its form against 

 sharp shocks, as we may test by shaking the 

 dewdrops on flowers, or observing the drops 

 from a fountain thafc run across the surface of 

 the water like pearls for some distance before 

 coalescing with the main body. In the air the 

 rain-drop is always perfectly round, as the 

 camera shows us, even if it were not a necessity 

 of that phenomenon, the rainbow. 



The size of the drop is doubtless dependent 

 upon the amount of surplus moisture in the 

 cloud. This in turn is dependent upon the 

 temperature of the air and the extent to which 

 this temperature has been reduced. Doubtless, 

 too, the suddenness of condensation has some- 

 thing to do with thp size ; and besides that the 

 drop in falling probably unites with other 

 drops, somewhat as globules of mercury co- 

 alesce, or a rain-drop running down a window- 

 pane gathers other drops in its downward 

 course. That the temperature has much to do 

 with the quantity of vapor in the cloud, and 



