WHICH RAINDROPS AND HAILSTONES ARE FORMED. 55 



That the temperature of the cloud exercises great influ- 

 ence on the character of the hailstones cannot be doubted ; 

 and if, as has been suggested by M. L. Dufour, the particles 

 will sometimes remain fluid, even when the temperature is 

 as low as o° F., it is clear that as they are swept up by a 

 falling stone they may freeze into homogeneous ice, either 

 in a laminated or crystalline form. Upon these questions, 

 however, I do not wish to enter, as they have no bearing 

 on the question as to the manner in which the mass of the 

 stone is accumulated; and I only mention them to show that, 

 if there are unexplained peculiarities, there are also causes 

 the efi'ects of which have not as yet been fully considered. 



This view of the manner in which hailstones are formed 

 at once suggests that raindrops may be formed in the same 

 way ; nor does there appear, on further consideration, to 

 be any reason to suppose that such is not the case. 



Of course a raindrop shows none of the structural pecu- 

 liarities of the hailstone ; and consequently we have not the 

 same evidence of the manner in which raindrops are formed; 

 but the explanation is sufficient, and there is apparently 

 no other. 



Raindrops cannot possibly have grown to the size with 

 which they reach the earth by the condensation of the 

 vapour of the air which they pass through, for the same 

 simple reason as that just stated for hailstones, namely 

 that there is no way in which the heat developed by con- 

 densation can be got rid of. The fact that the upper re- 

 gions of the air from which the drops start are colder than 

 those through which they descend, might, as has been 

 supposed, cause the drop to grow by condensing vapour in 

 the air through which it passes — but, as was shown by Mr. 

 Baxendell^, only to a very small extent, and one the limit 

 of which may be easily estimated. 



* Memoirs of the Lit. & Phil. Soe. of Manchester, vol. i. 3rd Serii's, p. 399. 



