696 Transactions of the American Institute. 



occurred in a dry electric condition of the atmosphere. If it be 

 objected that, in the presence of so much conducting material, the 

 metallic boiler with its metallic connections and surroundings, the 

 electricity cannot accumulate to the extent of surcharging the sur- 

 face, we may refer to what takes place in the thunder cloud for 

 answer ; where, although the watery globules, which fill the air and 

 compose the clouds, constitute a highly conducting medium for 

 diffusion, yet the surcharges do there occur, and cause very numerous 

 and frequent discharges of electricity in the form of lightning. It is 

 the superabundance of electricity in accumulation that sufficiently 

 accounts for the phenomena. Indeed, the thunder storm so well 

 illustrates our theory, that we must refer to its action at some 

 length. 



How clouds are formed and how they are sustained at their various 

 altitudes above the earth, are questions not without difficulty. As 

 water is far heavier than common air, and the clouds are composed of 

 watery globules, why do they not fall to the surface, like dew, instead 

 of ascending in the atmosphere ? In some way the effect of their 

 specific gravity is overcome, so as to keep them suspended at their 

 elevated levels. We may infer that these globules are filled with a 

 vapor lighter- than common air, which cause them to rise until they 

 reach an elevation where their weight is equal ; but of what that 

 vapor consists, besides rarefied air, we will not stop to explain ; not 

 because we concur with the French meteorologist, M. Pouillet, that 

 the data are too few to render the attempt advisable, but because it 

 is not necessary to the present inquiry. 



A distant view of the clouds discovers a great variety in their posi- 

 tions, forms and movements. In Nicholson's Journal of Natural 

 Philosophy they are classified according to their forms, and denomi- 

 nated cirrus, cumulus, stratus, cirro-cumulus, cirro-stratus, cumulo- 

 stratus and nimbus. Some of these forms are among the most 

 gorgeous and beautiful of visible objects, especially when irradiated 

 by the -rising or setting sun. But as we are about to speak of the 

 thunder-storm we shall confine our attention to the cumulus, which 

 is its peculiar theater, where, 



in explosion vast, 



The thunder raises his tremendous voice. 



This is the cloud which grows and increases from above in dense, 

 convex or conical heaps ; its masses are often of enormous proportions, 

 of great elevation and every variety of outline. It has the appear- 



