1882.] .«-0< [Lewis. 



lower than some thirty degrees above the southern horizon. At 12.20 

 Arcturus occupied almost the precise centre of the corona. 



At 12.25 the remarkable sight was presented of two hyperbolic curves of 

 light, the larger one lying in the north, the smaller to the south of the co- 

 rona, and each pointing in an opposite direction to the other. The smaller 

 hyperbola was bounded by an inverted arch of light in the south, some 30 

 degrees above the horizon. Straight lines of light, like a conjugate axis, 

 passed east and west from the central point between the hyperbolas. The 

 definite boundary of the southern auroral curtain may furnish data for a 

 determination height of the aurora above the earth's surface. The appear- 

 ance of the sky at this time is rudely represented in Fig 2. 



It is evident that the phenomena now seen was no mere effect of per- 

 spective. The auroral streamers had become curved in obedience probably 

 to the laws of magnetic force around a pole. 



At 12.35 the corona was near R. A. 215°, Dec. 20° 30', and atl2.'45 near 

 R. A. 2160 Dec. 20° 30'. At times the corona was a perfect star-like 

 crown, with a small white cloud of light in the centre. Sometimes, how- 

 ever, it would vanish completely for a few moments, to reappear with 

 greater brilliancy. The curdled cloudy matter within it occasionally took 

 fantastic curved forms, and at the same time the surrounding streamers 

 would form curves at their extremities close to the corona. Once the 

 streamers above and 'below the corona moved for a short space slowly 

 around it, in the direction of the hands of a clock. 



At 1.05 A. M. the corona was estimated at R. A. 224°, Dec. 20°, and at 

 1.10 at R. A. 226°, Dec. 20°. By this time it had become fainter, and it 

 frequently disappeared for a period. The aurora in the north continued 

 until daylight. Special attention was directed to mapping at intervals 

 during the continuance of the corona, its exact position among the stars, 

 in order, if possible, to determine any proper motion of its own. The cen- 

 tral point could always be determined by projecting the paths of streamers 

 to their converging point. 



The following map represents the approximate successive positions of 

 the centre of the corona, and the time of each observation. With the ex- 

 ception of the position given for 11.40 P. M., which was estimated from 

 memory, the positions here given are as plotted at the time upon the star- 

 map. 



Upon examination of this map it is at once evident that during the two 

 hours in which it was observed, the corona had an eastward motion through 

 space, and that this motion was at the rate of 15 degrees an hour, or pre- 

 cisely the direction and amount of the earth's rotation upon its axis. It 

 was as if the corona had been fixed permanently to the earth, and the ob- 

 servation is a strong confirmation of the theory that the aurora is a truly 

 terrestrial appendage.* 



* The writer has previouslv (v. Proc. A. A. A. S., Boston, 1880, vol. xxix., p. 245), 

 described a phenomenon noticed in the aurora of May 2, 1877, which, though less 

 conclusively, leads to the same deduction. In that case an auroral comet-like 

 streamer remained in a constant position, with regard to certain trees, for the 

 space of nearly an hour, being apparently fixed to the earth like a great pointer, 

 while the stars and the zodiacal light revolved past it. 



