ATMOSPHERIC ELECTRICITY. 371 



M. Arago is applied without difficulty to the effects which lightning 

 produces in wood, it does not appear to be the same when we seek 

 to give account of the transfers effected by the lightning. It is diffi- 

 cult to conceive how the sudden vaporization of a small quantity of 

 water placed in the fissures of the body is capable of detaching the 

 fragments of a weight of more than two hundred pounds and to send 

 them fortli to a distance of nearly two hundred feet, as observation has 

 often proved. It is also by having recourse, as M. Pouillet has done, 

 to electrical attractions that M. Peltier"^' explains tliis last phenomenon. 

 It is known that this philosopher regards a thunder-cloud as having 

 two distinct electrical tensions : the tension of free electricity at the 

 surface, and that of electricity retained at the surface of each of the 

 vesicles of vapor. This latter electricity not being able to participate 

 in the igneous discharge produced by the former, since it never 

 leaves the inside of the cloud, continues to act by its tension on terres- 

 trial bodies, and maintain them, in a free state of contrary electricity. 

 It is this powerful tension of attraction which, after the igneous dis- 

 charge caused by the nuturalization of free electricity, produces, ac- 

 cording to M. Peltier, the raising and transportation of the heavy 

 objects vv^ith which the strokes of lightning are very frequently at- 

 tended. 



[The simple explanation of the phenomena is that the air in the 

 path of the discharge is instantaneously endowed with an intense re- 

 pulsive energy, which causes it to expand with explosive violence, and 

 thus produce the observed mechanical effects. J. li.] 



Our object being to state only the principal effects of lightning we 

 shall add but a few words on the disastrous effects which are produced 

 when the discharge strikes men and animals. Observation teaches 

 that it kills them, either by producing lesions in the organs and in 

 the vascular system, or by paralyzing the nervous system ; they tlien 

 quickly undergo putrefaction, as is the case with all bodies sufier- 

 ing a violent death. But it sometimes happens that individuals are 

 struck with lightning without being killed, while other persons are 

 known to be killed by liglitning without being directly struck. The 

 former fact is to be explained by the consideration that organic bodies 

 being partial conductors, the electric matter may glide over their 

 surface without entering their interior ; while the latter is referred to 

 the effect known by the name of the return stroke, the result of 

 a violent action wliich takes place in the ponderable elements of 

 bodies, by the sudden recombination of their natural electricities decom- 

 posed by the electric induction of the thunder-cloud. Finally, it is 

 sometimes the case that lightning sets fire to light clothing on an 

 individual without causing any sensation of burning. This phe- 

 phenomenon is explained by the property which the electric fluid has 

 of setting fire to all fine substances which enter easily into combus- 

 tion, and of rarely kindling solid substances. 



-' Observations efc Piocherclics expeiiinentalos siirles Causes qui concourcnt ;i la formation 

 des trombes, page 94; and Coinptos llcndus, torn. X, page 202. 1840. 



