174 Mr Charles Tomlinson on 



trical states, when the attractions and repulsions are performed 

 with great celerity, and the hailstones, being equally active, 

 produce that peculiar noise that precedes a fall of hail 19 . 



Volta's theory has frequently been discussed, and objected 

 to on many grounds. JBecquerel points out the mistaken 

 notion that vapour in the act of forming becomes negative, 

 and while being condensed positive. When a dense cloud is 

 acted on by the sun, vapour arises charged with the same 

 electricity as that of the cloud ; but when, on reaching an 

 upper and colder region, it becomes condensed, it is said 

 to assume an opposite kind of electricity. But the clouds are 

 not electrified after this manner, seeing that electricity is not 

 set free by change of state, unaccompanied by decomposition. 

 Moreover, the question arises why the two clouds in opposite 

 states, connected as they are admitted to be by conducting 

 particles of vapour, do not immediately neutralize each other. 

 The oscillations of the hailstones between the two clouds could 

 only take place if the clouds were solid planes, as in the expe- 

 riment with the dancing pith figures. Then, again, the snow- 

 flakes which form the nuclei of the hailstones are said to be 

 formed at the upper surface of the lower cloud, and hence 

 must form a portion of it ; how, then, can they be driven out 

 of it without breaking up the whole cloud ? Even supposing 

 them to have reached the upper cloud, they must form an 

 integral portion of it, and can escape from it only by their 

 weight, and falling upon the moist surface below must be 

 detained there, as in the dancing-figures experiment, if, 

 instead of the lower metal plate, a surface of water be sub- 

 stituted, the adhesion between this and the pith figure is so 

 great that further motion ceases. 



It will be remarked that in Volta's theory the action of the 

 sun in promoting the evaporation of the cloud is all important. 

 This might be admitted if hailstorms occurred only by day ; 

 but such storms may occur at any hour of the night as well as 

 of the day. Kamtz has collected a long list of nocturnal hail- 



19 The sound that precedes the fall of hail is supposed to he due, not 

 only to the rattling of the stones against one another, but also to the fierce 

 wind from all quarters that usually accompanies a hailstorm. The sound 

 has been variously compared to the rushing or roaring of waters, as when 

 Morier, in Persia, thought that the river had suddenly swollen into 

 a torrent. Kamtz likens the sound to the rattling of a large bunch 

 of keys ; Peltier to that of a flock of sheep galloping over a stony road; 

 Daniell to the emptying of a bag of walnuts. Others speak of the noise 

 as crackling,, chattering, clashing ; and Volta regarded it as one of the 

 strong proofs of his theory. It should also be stated that the noise has 

 been attributed to the combination of the individual sounds produced by 

 each hailstone cutting the air with great swiftness. 



