520 THUNDER-STORMS. 



! and still remains unexplained. Succeeding philosophers have accomplished 

 ' little more than exhibiting, by direct experiments, and by the comparison oi 

 numerous observations, analogies which throw more or less light on the rela- 

 tions between the appearances which are exhibited in the atmosphere and 

 those general laws which have been deduced from experiments made on arti- 

 ficial electricity. 



The luminous appearances which attend the electrical discharges in the at- 

 mosphere, and which characterize the different kinds of lightning, must be re- 

 garded as explicable on the same principles as those of artificial electricity ; and 

 the various hypotheses and conjectures, more or less plausible, which have 

 been proposed to account for the one must equally be brought to bear on the 

 other. 



To regard the principle which darts through space with the enormous ve- 

 locity which the observations of Professor Wheatstone have shown lightning 

 to be endowed with, as ponderable matter, is extremely difficult. If it be pon- 

 derable matter it must follow the path of projectiles, and, consequently, its course 

 must be curved with a concavity turned toward the earth, except when it fol- 

 lows the vertical direction. In the zigzag path of cuspidated lightning there 

 is nothing analogous to this. On the other hand, such rapid and rectilinear 

 motions are quite consonant with the supposition of a system of undulations 

 propagated through a highly elastic medium, and are in all respects analogous 

 to the actual phenomena of light. The bi-cuspidated lightning finds its obvi- 

 ous type in the double refraction of crystallized media, and the heterogeneous 

 matter suspended in different strata of the air through which the lightning is 

 transmitted completes the parallel. 



The undulatory hypothesis is, nevertheless, beset with its own difficulties. 

 How can the pulsations of an imponderable ether be reconciled with the me- 

 chanical effects of lightning ? The analogy to the phenomena of light fails 

 when it is considered that, notwithstanding its velocity of 200,000 miles per 

 second, light has never acquired in its motion, even when condensed by the 

 largest burning reflector, sufficient momentum to affect in any sensible degree 

 the lightest substance suspended in vacuo by a filament of spider's web, while, 

 on the contrary, the electric fluid, issuing from the clouds, splits rocks, over- 

 turns the most massive structures, destroys gigantic trees, and projects to a 

 distance enormous weights. 



But of all the forms under which the results of electrical explosions in the 

 air present themselves, the most inexplicable is that of ball-lightning. Obser- 

 vation seems to countenance the supposition that these globes of fire are real 

 agglomerations of ponderable matter formed in the regions of the air by some 

 unexplained process. Where such formations are made ; whence proceed their 

 $ ponderable constituents ; what is their nature ; what sustains them in the air ; 

 / and what causes finally precipitate them ; are questions before which science 

 \ is mute. 



^ The constituents of the atmosphere are oxygen and azote, in the proportion 

 ' of four parts by weight of the former to fourteen of the latter. If the electric 

 ( spark be transmitted through a mixture of these two gases confined in a glass 

 ^ tube, a portion of the oxygen will combine chemically with a portion of the 

 J azote, and nitric acid will be formed. What the electric spark does in such a 

 S mixture the transmission of the electric fluid accomplishes in the atmosphere, 

 ( and nitric acid is formed, distinct traces of which are discoverable in the rain 

 which falls in thunder-storms. If, then, this power of determining the chemi- 

 cal combination of these constituents of the air be undeniable in this case, we 

 cannot reject the possibility of other combinations being effected by the same 

 agency. Besides oxygen and azote, the proper constituents of pure atrao- 



