Thunder unaccompanied rvith Ligliining, 91 



liancy^ descended from the clouds to the earth, at a little dis- 

 stanee from the external surface of the water-spout, or pro- 

 bably along that very surface itself ; and notwithstanding, ah- 

 solutely no detonation was heard.'* 



The thunder aoai7i which occni's without lightning may very 

 readily be explained. Suppose there are two distmct strata of 

 clouds, and that the one is superimposed upon the other ; sup- 

 pose that the upper stratum becomes the centre of a great 

 storm, that it is furrowed by brilliant lightning, and gives out 

 many loud resounding thunders. If the lower stratum of 

 clouds is very opaque or very thick, the lightning''s glare, how- 

 ever vivid, will not be afile to traverse it ; nearly the whole of 

 it will be absorbed ; and no sensible portion of it will reach the 

 surface of the earth, whilst, at the same time, as bodies which 

 are impermeable to light still easily allow the transmission of 

 sound, the same individual who most distinctly hears the thun- 

 der may see nothing of the lightning. The two-fold supposi- 

 tion that the strata of superimposed clouds exist simultaneously 

 at different elevations in the atmosphere, and that a storm may 

 Ta-ge only in tiie upper one, might, if required, be supported 

 by the narratives of so many credible travellers as to leave no 

 manner of doubt that we have indicated one of the causes 

 of the occurrence of thunder without lightning. I say, how- 

 ever, only one of the causes, for instances of thunder-bolts are 

 not rare, which apparently do not take their rise in the clouds, 

 and which detonate violently without being announced by any 

 luminous phenomena. 



Concerning ordinary thunder^ — 4he time between it and the light- 

 ning^ — its peals, — thunder-claps, — the extreme distance at which 

 it may be heard, — the thunder of serene weather, and of the 

 length of the lightning' s flash. 



Sometimes the thunder is not heard till a cmisiderablc tirnv 

 ajier the flash. This requires some explanation; for no one 



* This absence of noise in ilio midst of such dazzling irradiations, is ii 

 plienomenon which has not been noted by meteorological observers. Mr 

 Griswold believed, that, in reality, there was sound as in a common storm. 

 He argues that the rapid whirling motion of the air which constitutes the 



