332 Scientific Intelligence. 
nucleus, but continuing to follow a nearly similar course at each new dis- 
charge from its surface. 
The most natural inference from this would seem to be that the nucleus, 
if it rotates at all upon an axis, does so very slowly. Of the pendulum- 
like vibrations of the luminous sectors ascribed by Bessel to the comet of 
Halley, nothing was seen; although the opportunity of witnessing them, 
had they existed, was very favourable, as the sectors were well displayed. 
The nucleus was throughout brilliant, and, to appearance, solid, with 
a diameter of from 2” to 3”. 
The disposition of the nebulosity, in the part of the tail contiguous 
to the head, was nearly uniform throughout; the axial darkness being 
scarcely distinguishable, excepting on one occasion, July 34d. 
The following positions have been derived from comparisons with 
neighbouring stars :— 
1861. Oee Wee a 3 
July 2, . . Sb 28m 3gs Sh 37m 434.92 = 4. 62° 51/171 
Rey aN oe 9 49 15 85 66 6 15°3 
Ss...) te eo. Be 9 56 668 66 16 05-1 
ee, Hobe ae) os Ho J48 66 53 26-4 
Se eee Be it? 57” Bey 66 3 22-0 
eae Bn ar Ba) ae) 12 21 2°60 64 51 33°3 
Hakan sate Os ied og 13 21 36-05 61 46 13-7 
Ta ee ae” ay 13° 87 ‘37 ‘ge 60 21 45-2 
PIG Die gyn! Fo 13 49 26-80 59 9 34-1 
Se mM SR a 2 14. 8 0°59 56 64 47-2 
So | RRR: ae te 14 13 59-24 56 5 25°7 
The nucleus admitted of very precise observations;-indeed it is a 
curious fact, that it would be quite possible, by means of proper com- 
parisons with neighbouring stars, to obtain the differences of terrestrial 
longitudes of the principal points at which it was observed, with a de- 
gree of precision only surpassed by the more refined methods known in, 
astronomy. . 
The near approach of the present comet to the earth, and the sharply 
defined point of its nucleus, illustrates the practicability of a method of 
determining the solar parallax with perhaps greater exactness than can 
be attained by any other means. Many comets have stellar points for 
their nuclei, visible in the larger telescopes, which admit of as accurate 
comparisons with neighbouring stars as is practicable in measurements 
among the stars themselves. Many such have appeared within the last 
fifteen years. Suppose such a comet to be suitably placed so as to be ob- 
served simultaneously in different quarters of the globe, when at a dis- 
tance from the earth of less than one-twentieth of the sun’s distance : 
under favourable circumstances it would not be hazarding too much to 
say, that in the course of its apparition the probable error of the solar — 
parallax could be reduced within smaller limits than is possible by means 
of transits of Venus or of any other method. Such an opportunity might 
possibly afford an improved value of the mass of the earth. 
The following elements of the comet have been computed at the Obser- 
vatory by Messrs Safford and Hall :— 
Elements of Comet II., 1861. By T. H. Sarrorp. 
T = 1861, June 11.1878 Cambridge m. t. 
log. gq= 9-91299 
r—Q= 329° 10/81 
Q = 278 59 +28 
i = 85 41:43 
Motion direct. 
