Remarks on the Tuils of Halley’s Comet. 331 
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 
night 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 Kénigsberg on the 13th and 14th, the sector 
was still more Juminous 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 diferetice 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. 
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 magnetie properties by a 
* Vol. XXXL. p. 149. + Bib. Univ. p. 360. 
