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the electric discharge takes place, it acts on the atmosphere 
precisely as a descending solid would do of an area equal to 
that occupied by the electric current. It drives before and 
to either side of it the particles of air, vapour, and whatever 
else is contained in the atmosphere, and owing to its enor- 
mous velocity, leaves its path a vacuum. The departure of 
the electricity from the storm cloud causes a simultaneous 
condensation of the vapour formerly upheld by electric 
influence, which now rushes down to the earth through 
the vacuum left below it. The velocity with which these 
drops of water descend may be almost inconceivably great. 
The form of the hailstones I have described, shews that while 
in a fluid state they had a rotatory motion around their own 
axes, in addition to the downward one due to electricity and 
gravity. This rotatory motion I conceive takes place at the 
earliest period of their descent towards the earth, during the 
time they are passing out of the cloud into the vacuum below 
it. In this double motion of enormous rapidity in a vacuum, 
we have the conditions of an evaporation quite adequate to 
the conversion of drops of water into hailstones. In this 
matter, however, we are not left altogether to inference. An 
account of what took place during a balloon ascent in France, 
seems to explain it. The Aeronaut left the earth, at Paris, 
June 18, 1786, Barometer 29, 68, Thermometer 84°. 
After descending once he again rose, and heard thunder 
beneath his feet, He then approached the earth a second 
time, but almost immediately rose to an elevation of 2,400 
feet, Thermometer, 66°. He then descended for the 
third time, after which he left the earth at 8 p.m., and passed 
upward through a dense body of cloud, in which thunder 
followed lightning in quick succession, and the Thermometer 
fell to 21° ; but when he had reached an elevation of 
3,000 feet, and had passed beyond the region of electric 
disturbance, it regained its position of 66 6 . He re- 
