28 
The striae were strongly marked, and exactly resembled 
those of the hailstone. The bases also were rounded. 
They were somewhat steeper than those of the hailstone ; 
but this was clearly due to the want of sufficient 
cohesive power on the part of the plaster. It was not suf- 
ficiently wet. Owing to this cause also it was not possible 
to preserve the lumps when they were formed, as the least 
shake caused them to tumble in pieces. 
I also tried a jet of the vapour of naphthaline, which at 
ordinary temperatures is solid, driven by means of a cross blast 
of air against a small object, and in this way I obtained masses 
closely resembling hailstones, but these also were too fragile 
to bear moving. At ordinary temperatures the powdered 
naphthaline does not adhere like ice when pressed into a 
lump. No doubt at very low temperatures ice would behave 
in the same way — that is to say, the particles would not 
adhere from the force of impact. Hence it would seem 
probable that for hailstones to be formed the temperature of 
the cloud must not be much below freezing point. 
That the effect of the temperature of the cloud exercises 
great influence 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 tempera- 
ture is as low as 0° 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 effects 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. 
