186 TERllESTEIAL PHENOMENA. 



without ever hearing a noise. Even if it be considered that 

 this negative evidence ought not to countervail the positive 

 testimony of two observers, Hearne at the mouth of the 

 Coppermine River, and Henderson in Iceland, it must be 

 remembered that Richardson and Hood heard, indeed, a 

 sound, which one terms " a hissing noise, like that of a 

 musket bullet passing through the air/' and of which the 

 other says, " that it resembled the noise of a wand waved 

 smartly through the air ;" but though both were inclined to 

 regard these sounds as connected with the Aurora, each adds 

 that they were attributed "by Dr. Wentzel to the con- 

 tracting of the snow from a sudden increase of cold " and 

 this opinion was supported "by the same sounds being 

 heard the following morning/' (Pages 585 and 628 of the 

 Appendix to " Eranklin's First Journey to the Polar Sea/') 

 Wrangel and Giesecke arrived at the same persuasion, thai 

 sounds heard during Auroras do not proceed from them, 

 but are to be ascribed to contractions of the ice, and of the 

 crust on the surface of the snow, from sudden increase of 

 cold. The belief of a crackling noise did not originate 

 with uncultivated persons having frequent opportunities of 

 noticing the Aurora, but with learned travellers ; the cause 

 probably being, that as electric flashes in spaces filled only 

 with a very rare atmosphere had been observed to resemble 

 the northern light, the latter phenomenon was regarded as 

 an effect of atmospheric electricity, and thus people 

 heard what they expected they ought to hear. Recent 

 experiments, however, with regard to atmospheric elec- 

 tricity, made with very sensitive electrometers, have hitherto, 

 contrary to all expectation, given only negative results, since, 

 during the finest Auroras, no change has been detected. 



