and on certain correlative Phenomena. 345 



comes visible, is in general overlooked, the visual ray of the 

 stream itself being intercepted by the earth's rotundity, or by 

 an extended horizontal volume of dense vapours. It may be 

 further observed, that those supposed silent gleams are never 

 seen in the zenith nor close to any one, and that when the 

 rains approach sufficiently near, the electric stream itself be- 

 comes visible, and thunder audible, at first very low, but 

 louder as the distance diminishes. 



The northern lights (which are doubtless electric) are at- 

 tended with a loud crackling noise, which, in America, is often 

 experienced as low as 44° north, as I have witnessed at Bath, 

 New Hampshire, in the months of December and January, 

 especially in the winter of 1758-9. This happens only in the 

 most severe cold; but thunder-storms and heat lightning, so 

 called, chiefly occur in the hottest season, or about the month 

 of July. It would hence appear that both a high degree of 

 heat and great cold are favourable to the production of atmo- 

 spheric eiectricity: its explosions in the latter case (that of 

 the aurora borealis) seem to be greatly diffused, and sound 

 like numerous sparks elicited by the electrical battery. 



It would seem, in such cases, that the electric fluid, being in 

 a manner insulated by the frozen surface, and its evolution 

 from the earth thus intercepted, becomes, in the absence of 

 aqueous vapour and gaseous emanations, incapable of con- 

 densation, so as to form an explosive current: and in such 

 condition — the earth being sealed by frost — a thunder-storm 

 was probably never known to happen. 



A brief quotation or two may serve concisely to exhibit the 

 exceedingly vague ideas entertained on the present subject. 



" In a serene sky, the lightning in this country at least, al- 

 most always hath a hind of indistinct appearance without any 

 determinate form, like the sudden illumination of the atmo- 

 sphere occasioned by firing a quantity of loose gunpowder ; but 

 ■when accompanied with thunder, it is well defined, and hath 

 very often a zigzag form that which appears like indi- 

 stinct Jlashes, whose form cannot be readily observed, is seldom 

 or never known to do hurt."— Encyc. Brit., Art. Lightning. 

 "The reason why this kind of lightning is never attended with 

 any report, is, that there is no particular object against which 

 the force of the flash is directed. ...A flash of lightning, how- 

 ever limited its extent may appear, diffuses its effects over a 

 great space of atmosphere, for, after one of these silent flashes; 

 it is no uncommon thing to observe the sky become obscure 

 though it had been quite serene before." — Encyc. Londinensis, 

 Art. Lightning. These remarks, although but an echo of 

 established opinions, appear altogether too puerile and absurd 

 to require any comment. 



Third Series. Vol. 4. No. 23. May 1 834. 2 Y 



