-1859] WRITINGS OF JOSEPH HENRY. 297 



adopted. If several large drops of water come in contact, 

 and by their attraction rush into one larger drop, and if 

 this be borne up so high that it begins to freeze, crystal- 

 lization will commence at the surface, the air in the water 

 will be driven inward as the solidification proceeds, and 

 when the freezing is completed it will give a spongy appear- 

 ance to the nucleus of the hail stone. As the hail stone is 

 carried up a second time it will gather in its ascent another 

 quantity of water which will again begin to freeze and pro- 

 duce the spongy envelope, inclosing the stratum between it 

 and the coat of jDure ice, surrounded by a stratum of solid 

 ice, and so on. The number of concentric envelopes will 

 indicate the number of times the hail stones have been 

 carried up, and the collision of the stones in their ascent and 

 descent will give rise to the peculiar noise which is heard 

 during the passage of a storm of this kind. 



The ascent of bodies in the centre of the up-moving column, 

 and their being thrown out at the top, is not a mere matter 

 of speculative inference, but rests upon direct observation. 

 Bodies are seen to be carried up in the middle of the ascend- 

 ing column and throv\m out as we have described; but above 

 all Mr. Wise, the celebrated aeronaut, gives an account of 

 what took place on the occasion of his balloon being drawn 

 into the ascending column of a thunder storm. The balloon 

 was carried up to a great height, thrown out on one side, 

 sunk gradually down, was caught again by the in-blowing 

 current which was rushing in to supply the column, again 

 violently carried up, and again thrown out, and this several 

 times in succession. 



We have here, in accordance with the theory of Mr. Espy, 

 a true, simple, and sufficient explanation of the production 

 of hail, which takes place in the hottest and most sultry 

 weather, when the air is most highly charged with moisture, 

 and consequently when it contains the greatest amount of 

 latent ascensional power. The vapor which ascends is de- 

 rived from the moisture which a short time before existed at 

 the surface of the earth, and since the ascending column 

 usually carries up with it a quantity of fine dust, gravel, 



