Remarks on the Tails of Halleyh Comet. 831 



its atmosphere, and have a relation to certain magnetic poles of the 

 nucleus. 



It may perhaps be worthy of consideration, that if the earth had 

 an atmosphere as extensive as that of Halley, and only one north 

 magnetic pole, a terrestrial aurora borealis completely circumpolar 

 and sufficiently brilliant to be seen at the distance of the comet, 

 would have appeared from that position as a conical tail, and its axis, 

 being in the magnetic axis of the earth, would have appeared like 

 that of the cone of Halley to revolve around the earth's astronomical 

 axis. A greater number of poles might render the tails more nu- 

 merous or irregular, as in the comet of 1825. In either case they 

 might occupy fixed situations on the surface, their axes making con- 

 stant angles with the axis of rotation. This hypothesis would allow 

 real and simultaneous variations in length and brilliancy, and such a 

 diminution of the latter at the edges as was observed here on the 

 16th of October. At Konigsberg on the 13th and 14th, the sector 

 was still more luminous than on the 12th, the day of the comet's 

 perigee, and could be distinguished even to the distance of 45" 

 from the comet's center. On the 12th the distance was 30'^ On 

 the 13th it was stated here, in the journal published in the last num- 

 ber,* that it appeared to extend three or four times as far from the 

 nucleus as it did the preceding evening. These observations tend 

 to establish the fact of a real augmentation of angular length, though 

 the amount differed from difference of atmosphere, &;c. What was 

 meant by nucleus was immediately explained. No real nucleus was 

 at any time seen ; and this accords with M. Bessel's observations.f 



In regard to the class of ordinary tails, they remain, notwithstand- 

 ing the rotation of the nucleus, nearly opposite to the sun ; perhaps 

 by the agency of some repulsive force of an electrical or magnetic 

 nature emanating from it. Is there any evidence that the material 

 of these ever assumes its determinate direction until it has risen to 

 some distance from the surface of the nucleus ? May not this be in 

 part referable to the diminution of gravitation or the coercive force of 

 the nucleus, as the vapor in consequence of its elasticity and buoy- 

 ancy departs in all directions from the nucleus, till at length its grav- 

 itation toward the nucleus is overcome by the repulsive force ema- 

 nating from the sun ? And may it not be also in part referrable to 

 the development of electrical and perhaps magnetic properties by a 



* Vol. XXXI. p. 149. t Bib. Univ. p. 360. 



