134 



The corona formed again at nine ; and, though again broken, was 

 imperfectly visible after that time. 



At half past nine, the eastern portion of the sky became tinted with 

 intense red and green ; but at half past ten, little else remained than 

 the appearance of bright horizontal beams of a white colour in the 

 north. 



If it be admitted that the centre of the aurora was precisely midway 

 between a. Aquilse and a, Lyrse, at twenty minutes past eight, its azi- 

 muth must have been 1° 14' 42" E. of S., and its altitude 73° 27' 6"; 

 the latitude of the observer being 40° 20' 47" N. The point thus 

 designated, would be very nearly in the direction of the dipping 

 needle; the dip being, by observation, 72° 47' 6" (72° 47.1') and 

 the variation (though not accurately determined,) some 4° W. or 

 that of the S. end of the needle, of course, the same extent to the east. 

 The degrees of azimuth, reckoned on a parallel to the horizon at an 

 altitude of 72° and more, being small, the deviation from the direc- 

 tion of the dipping needle, measured on the arc of a great circle, would 

 be scarcely more than 1° towards the N. W. 



Professor Bache stated that his own observations near Philadelphia, 

 of the altitude of the apparent converging point of the auroral beams, 

 at nine, P. M. made it but about 69°. He had witnessed a case of 

 the appearance of a dark spot of irregular shape, between two beams 

 of light, which was certainly not a cloud, as the stars were not at all 

 obscured by it, and which he' supposed to be the phenomenon referred 

 to recently by Professor Lloyd. No mottled clouds, such as usually 

 attend the aurora, were visible during the period between nine and 

 ten o'clock, when he had been able to observe. Professor Bache 

 stated that he did not place much stress upon his measurements, as 

 he had been prevented from sustained observation by indisposition. 

 There had been, in the newspapers, an account of an auroral display 

 visible at London, on the morning of the fourth of September, at 

 about the same absolute time as at Princeton, according to Professor 

 Alexander's observations. It was said to have been accompanied by 

 a very unusual number of shooting stars, compared in one statement 

 to the splendid display of November 13th, 1833. 



Professor Henry had examined the light of this aurora by the 

 polariscopes of Savart and Arago, but had not been able to detect 

 the slightest trace of polarization. 



The following extract from a letter, addressed by Professor 

 Henry, of Princeton, to Professor Bache, was read, announc- 



