254 Phetiamena and Causes of Hail Storms. 



indicates that the congelation began in highly rarefied air, such 

 being precisely the appearance of a drop of water frozen under 

 the exhausted receiver of an air pump *. And, finally, the sud- 

 den and severe cold weather which often immediately follows a 

 hail-storm, only indicates that the cold blast which produced 

 the hail, extends something of its influence even to the surface 

 of the earth itself. 



What is the cause of the small momentum of hailstones ? 

 Although hailstones, when large, do great damage to tender 

 crops, and occasionally kill small animals, yet, it is oo the whole 

 svu'prising that they fall with no greater force than they do. A 

 pebble of the same size falling from the mouth of a well, upon 

 the head of a man at the bottom, would kill him ; and the me- 

 teoric stones which fall from the sky, many of which do not ex- 

 ceed the size of some hailstones, bury themselves deep in the 

 ground, and sometimes penetrate through the entire body of a 

 house, and bury themselves in the cellar-f*. The small momen- 

 tum of hailstones is partly to be ascribed to their low specific 

 gravity, which is a little less than that of water ; but still they 

 are heavy enough to fall with a hundred times the momentum 

 which they actually exhibit, descending as they do through 

 many thousand feet. Their velocity is in fact very small, 

 whereas we should expect to find it immensely great ; the true 

 reason of this I apprehend to be the following. We are to re- 

 gard the largest hailstone as commencing its formation with a 

 small nucleus, and as receiving continual accessions of matter in 

 descending, until it reaches the ground. But the watery vapour 

 of which these accessions are composed, is matter at rest to be 

 put in motion by the falling body, which is therefore taking on 

 a new load at every stage of its progress, and consequently has 

 its speed continually retarded. The velocity which it acquires 

 in falling each successive moment, is lost by communicating mo- 

 tion to so large a quantity of matter at rest, as that which com- 

 poses its accretions. 



■ Leslie, Encydo. Ed. Meteorology. 



f See an amusing a< count of the force of falling hailstones by Fairfax, in 

 the 1st vohune of the Phil. Trans.* 



