702 Transactions of the American Institute. 



instantly undergo a violent explosion, which unites them in due pro- 

 portions by chemical affinity to compose water. Think how will the 

 facts agree with the foregoing statement. When a broad flash of 

 lightning is accompanied by a heavy roll of thunder, then follows 

 immediately a remarkable increase of the shower of rain, the precise 

 effect which must ensue from an explosion of those gases in the sup- 

 posed abundance and their chemical combination. The sound accom- 

 panying the flash is just such as would result from an explosion, 

 with a report much heavier than that of the loudest artillery. The 

 height from which the sound comes, it will be remembered, is from 

 half a mile to a mile and a half above us, and sound passes downward 

 with much obstruction. The heaviest reports are often heard when 

 the lightning evidently does not strike the earth. Usually the thun- 

 der is but a single report, and the rolling detonation is that sound 

 reverberated from the numerous heaps or masses of the cumulus. 

 This naturally and adequately accounts for the peculiar character of 

 the sound, which is heard, alike and the same, on the level plains of 

 regions without mountains or elevations of the surface, and over the 

 level of the sea. To ascribe the prolongation to the reflection of the 

 sound from the woods, the buildings, or the earth's surface, is hardly 

 justified by the. laws of acoustics, according to which such reflection 

 would be with an upward .rebound, and therefore inaudible to the 

 dwellers upon the surface. 



The lightning stroke which reaches an object near to us always 

 has a sharp, violent, clattering sound, often if not always followed, to 

 our preception, by the long, rolling reverberation of the distant explo- 

 sion. The former sound^though first heard, is really preceded by the 

 latter, which takes place on the explosion of the gases as the lightning 

 touches them in parting from the cloud ; and the latter is produced, as 

 before noticed, by the resistance which the lightning encounters in 

 its passage through the air to the earth. This double sound most fre- 

 quently occurs when the sharp and smaller sound from the lightning, 

 darting horizontally or upward from the clouds, as is often seen, is 

 not audible to us. It will be recollected that, in such instances, there 

 is a wide illumination of the cloud at the time the lightning appears 

 to dart forth from its bosom, and we hear only the heavy roll of the 

 thunder following. That blaze of light is the light of the explo- 

 sion ; the deep-voiced thunder is its report. It would seem, 

 then, that there are present in the thunder cloud all the agencies 

 requisite to the accumulation and development of electricity in 

 superabundance, as heat and moisture, violent collision of masses, and 



