Prof. Loomis on the Hail Storm of the first of July, 1853. 47 
It is believed that during the passage of a hail storm, the tem- 
perature of the upper air is considerably below the mean. he 
simple presence of clouds in the lower atmosphere would tend to 
produce such an effect. The atmosphere derives its heat from 
the earth, and is but little affected by the direct passage of the 
solar rays. The heat which the earth imbibes from the sun is 
continually thrown off by radiation ;—but when the surface of 
the earth is covered by a cloud, this radiant heat is intercepted, 
and the temperature of the lower air is thereby elevated a 
still night, the presence of clouds sometimes causes the thermom- 
eter to stand ten or fifteen degrees higher that it would otherwise. 
But if, by the interposition of a cloud, the lower atmosphere be- 
comes unusually hot, the atmosphere above the cloud must receive 
less than its usual supply of heat, that is, it must become unusu- 
ally cold. 
Moreover, in the storm of July Ist, the hail was formed in a 
current blowing violently from the northwest, which came there- 
fore from a higher latitude, and of course brought with it a dimin- 
ished temperature. I have no data sufficiently precise for estima- 
ting the effect to be ascribed to this cause, but I think we may 
conclude that at the time of the storm in question, at an elevation 
of 5000 feet above New York, the temperature could not have 
differed much from 32°. We have not however yet reached the 
temperature necessary to the. production of hail. 
Another source of cold is to be found in the evaporation from 
the surface of the hailstones. It is well known that if we tie a 
plece of thin.muslin upon the bulb of a thermometer, and then after 
dipping the bulb in water, swing it rapidly through the air, the 
thermometer will sink below the temperature of the air, several 
degrees, sometimes ten or fifteen; an effect due to evaporation. 
ring a hail storm, the hot air from the earth’s surface is carried 
by the upward movement to a considerable elevation, by expansion 
it is cooled, and a portion of its vapor is condensed. e drops 
thus formed at a temperature not, far from 32°, are still further 
cooled by evaporation from their surface, (the evaporation being 
promoted by their rapid motion ;) the remainder of the drop is con- 
gealed; and as new vapor is precipitated, it is congealed upon the 
water, like nearly every other substance, in passing to the sofid 
State, inclines to crystallization, the ball as it increases, does not 
generally retain the spherical form, but shoots out irregular prisms. 
ow does a hailstone remain suspended in the air long enough 
to acquire a weight.of half a pound? 
This difficulty is not, to my mind, a very formidable one. I 
Conceive that hail stones are formed with great rapidity. e 
vapor is condensed with great suddenness and almost instantly 
frozen. I think very large hailstones may be formed in five 
nate ar 
