24 
This appears to indicate the character of the difference 
between those conditions which result in snow and those 
which result in hail. 
When the clou a -particles are formed at or above the 
temperature of 32°, and then freezes, owing to cooling by 
expansion or otherwise, the particles as they freeze retain 
their spherical form. This is what happened in the spray. 
On the other hand, when saturated air at a temperature 
below 32° is still further 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 rain-drops, 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 
arguments 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 resem- 
bling in all particulars those formed by nature. And, in 
conclusion, I would thank Dr. Crompton for the suggestion 
of the means by which I have been able to produce these 
stones. 
