94 On the Formation of Hail. 
If, indeed, a middie stratum of cold air should occasionally 
intercept the falling rain in the Arctic circle, and convert it into 
hail, the common theory would appear more consistent ; but as 
this is not the case, I am inelined to attribute its formation to 
electricity, which so frequently manifests its presence during hail 
showers, by thunder and lightning, and which, like hail, is un- 
known in high latitudes*. 
Scarcely a year passes without injury being done to the crops 
in some part of Europe by hail showers, the stones of which are 
frequently as large as rousket balls, plums, eggs, &c.; and Dr, 
Halley records instances of their being thirteen or fourteen inches 
in circumference, and weighing from five ounces to half a pound, 
which I think favours the idea, that instead of acquiring such a 
magnitude in their fall by accumulations round the nuclei formed 
by drops of congealed rain, they are generated by some sudden 
convulsion of the atmosphere; particularly as we know that a 
great portion of the air through which they must pass, if not of 
a temperature to diminish their bulk, is at least so warm as to 
prevent the congelation of any particles of vapour they might 
have the power of condensing round them in their descent. Now, 
as hail occurs most frequently when the presence of lightning 
shows the atmosphere to be overcharged with the electric fluid, 
and does not occur at all in those latitudes where lightning is 
unknown, | am induced to suppose, that electricity may have the 
power of causing a sudden expansion of the air, and consequently 
of generating intense cold; whereupon the particles of vapour 
contained in that part of the atmosphere will be immediately 
condensed, a number of these condensed particles (facilitated by 
the expansion of the air) will, by the force of their own attraction, 
combine, forining large drops of water, which being frozen by 
the excessive cold generated, descend by the laws of gravity, and 
produce the phznomenon of hail. 
The appearance of the hail-stones (which seems to be the basis 
on which the common theory is founded) may, I think, be ac- 
counted for, by supposing that the central particles unite, and 
form drops of water before the expansion has reduced the at- 
mosphere to the freezing temperature; that these drops are af- 
terwards frozen, and constitute the icy centres, and that the less 
dense exterior coating is produced by the remaining particles 
being congealed before they are brought in contact. The size 
of the hail-stones may depend upon the degree of humidity and 
expansion of the air, the obstruction offered to the union of the 
* During the late Polar expeditions, neither hail nor lightning was ob- 
served within the Arctic circle, nor was the atmosphere ever sufficiently 
charged with the electric fluid to effect the electrometer. 
condensed 
