170 ON HAILSTONESj RAINDROPS^ AND SNOWFLAKES. 



all appearance they consist of an aggregation of small 

 spherical particles of ice ; and it seems worthy of notice 

 that^ while nothing like a snow crystal appears ever to be 

 produced in the ether spray, the moment the blast is stopped 

 the end of the ether tube becomes covered with ice, which 

 often assumes the form of snow crystals. 



This appears to indicate the character of the difference 

 between those conditions which result in snow and those 

 which result in hail. 



When the cloud-particles are formed at or above the 

 temperature of 32^, and then freeze, owing to cooling by 

 expansion or otherwise, the particles as they freeze retain 

 their spherical form. This is what happens in the spray. 

 On the other hand, when saturated air at a temperature 

 below 32° is still fuither cooled, the deposition of the vapour 

 will be upon ice, and will take the form of snow crystals. 



The aggregation of the snow crystals into flakes is, as I 

 pointed out in my previous paper, accounted for by the 

 larger crystals overtaking the smaller crystals in their 

 descent, and the still more rapid descent of the flakes as 

 they increase in size. 



As regards the formation of raindrops, I have nothing to 

 add to what was contained in my last paper. The same 

 explanation obviously applies to both hail and rain ; and 

 any doubt which may have been left by the less direct ar- 

 guments in my former paper will, I venture to think, have 

 been removed by the verification of my predictions in the 

 production of artificial hailstones so closely resembling in 

 all particulars those formed by nature. In conclusion, 

 I would thank Dr. Crompton for the suggestion of the 

 means by which I have been able to produce these stones. 



