714 Transactions of the American Institute. 



than in warm climates ; and that indicates that the phenomenon is 

 probably electrical. 



Dr. Van der Weyde — The center always corresponds to the mag- 

 netic pole, even when the magnetic variation is as much as 20°. 



Dr. D. D. Parmelee — Two things render it very improbable that 

 the aurora produces an audible sound ; its elevated position, and its 

 great attenuation. It extends to a great height ; and it is so attenu- 

 ated, that the stars are visible through it. It is highly improbable 

 that there could be much sound produced under such circumstances, 

 and still more improbable that the sound could reach the earth. 



The President — This gentleman was up in a balloon. 



Dr. Parmelee — He was not more than five miles high ; and the 

 aurora is stated to extend to a height of 700 miles. 



Dr. Yan der Weyde — A noise high up does not easily come down. 

 I consider the aurora as a thunder storm in a climate so cold that 

 that there is no water. Clouds are positively electric. In the far 

 north, where no evaporation takes place, the upper atmosphere becomes 

 charged with electricity. The medium above the planetary atmos- 

 phere is a good conductor of electricity ; and this electricity may be 

 discharged by the route to the equator through the rare atmosphere, 

 which may extend 300 or 400 miles high, The question is whether 

 the sound can penetrate the atmosphere so as to reach the earth. 



Mr. Hudson — Why is it, if the aurora is so elevated, that the cur- 

 rents affect the telegraph wires ? 



Dr. P. H. "Van der Weyde — By induction. They do not come 

 down. When you have a current through a wire, there will be an 

 induced current through a parallel wire, with any apparent connec- 

 tion. It depends on the variation of the current ; for if the upper 

 current is constant there is no lower current. 



The President — Induction is probably produced by a change in 

 the polarity of the atoms of the intervening atmosphere, or of the 

 ether which pervades the atmosphere. 



Dr. J. W. Kichards — Medical experts consider it settled that the 

 induced current has a different medical effect from the direct current. 

 With regard to the noise, if direct testimony is worth anything, I 

 stand here as a witness. In the middle of a pleasant September night, 

 when there was a very brilliant aurora spanning the whole sky, I 

 observed that, as the belt of light widened or narrowed, there was an 

 evident noise, almost simultaneous with it. I stopped my horse, and 

 spent about an hour in observing it. That was about the year 1830. 

 It might have been a wind which produced the effect upon the aurora, 



