350 WRITINGS OF JOSEPH HENRY. [1855- 



fore induced to adopt the conclusion that the earth — in rela- 

 tion to space around it, is permanently electrical; that perhaps 

 the setherial medium, which has been assumed as the basis 

 of electricity, as was supposed by Newton, becomes rarer in 

 the vicinity of — and within bodies of ponderable matter. Be 

 this as it may, all the phenomena observed in the atmos- 

 phere, and which have so long perplexed the physicist, can 

 be apparently reduced to order, and their dependencies 

 and associations readily understood, in accordance with the 

 foregoing assumption. This is not a mere vague supposi- 

 tion, serving to explain in a loose way certain phenomena, 

 but one that enables us not only to group at once a large 

 class of facts, (which from any other point of view, would 

 appear to have no connection with each other,) but also to 

 devise means for estimating the relative intensity of action, 

 and to predict both in mode and measure changes of atmos- 

 pheric electricity before the}" occur. It follows, as a logical 

 consequence from this theory, that salient points, such as 

 the tops of mountains, trees, spires, and even vapors, if of 

 conducting materials, will be more highly excited than the 

 general surface of the globe, in a manner precisely similar 

 to the more intense excitement of electricity at the summit 

 of a point projecting from the surface of the prime conductor 

 of an ordinary electrical machine. 



It also follows from the same principle that if a long 

 metallic conductor be insulated in the atmosphere, its lower 

 end, next the earth, will be positive, and the upper end nega- 

 tive. The natural electricity will be drawn down by the un- 

 saturated matter of the earth into the lower end of the wire, 

 which will there become redundant, while the upper end 

 will be rendered negative or under-saturated. That this 

 condition really takes place in the atmosphere was proved 

 in a striking manner b}'' the experiment of Gay-Lussac and 

 Biot in their celebrated aerial voyage, which consisted in 

 lowering from the balloon an insulated copper wire, termi- 

 nated at each end by a small ball. The upper end of this 

 was found to be negative, and consequently the lower end 

 must have been positive, since the whole apparatus — includ- 



