observed at the Summit of Den-Nevis. 31,5 



practice of the vulgar, sometimes find it more convenient to 

 wear their caps in their pockets. Several other gentlemen, 

 then, by uncovering their heads, gave their hair an opportu- 

 nity of exhibiting the beautiful phenomena of electrical attrac- 

 tion and repulsion. 



As to the state of the electricity of the mountain, with re- 

 ference to that of the cloud, nothing can be inferred from 

 these motions of the hair ; but the hissing noise seems to in- 

 dicate that it was positive, — that the electric fluid was stream- 

 ing from the mountain in pencils chai-acteristic of electricitv in 

 that state. 



Experiments would lead us to infer,* that when vapour 

 ascends into the atmosphere, it induces a negative state on 

 the surface of the ground, and theory would lead us to ex- 

 pect that the clouds in general are positive with respect to the 

 surface of the earth beneath them. But observation must 

 decide which of the two states prevails. Not only does the 

 phenomenon alluded to countenance the opinion that in this 

 instance the earth was positive, but we afterwards learned 

 that about the same time there had been a thunder storm at 

 Inverary, in the direction of which we heard two peals of 

 thunder, and that there the lightning was seen to ascend. 

 Of the possibility of observing the direction of lightning, at 

 least in certain cases, I think there can be no doubt. An 

 electrical discharge through a very long circuit of conductors, 

 is indeed simultaneous ; but when it has to pass through a 

 long column of dense air, I think a good eye, uninfluenced by 

 any theory, may be able to say, whether it was ascending or 

 descending, particularly if the mass of electric fluid was not 

 very great. This I had an opportunity of observing last 

 summer, during a lightning storm in Paris, when the ascent 

 of the electric fluid from several spires, and particularly from 

 the dome of St Genevieve^ was not less distinct, than the 

 form of the beautiful coruscations which flashed in the shape 

 of pencils from the conductors of the Thuilleries. A flame of 

 sheet-lightning, too, often condensed into a flash of forked 



• Davy's C/iem. Phil. \>. 138. 



