60 D. Kirkwood—Origin of Comets. 
Art. VIII.—WNote on the origin of Comets ; by DANIEL 
KIRKWOOD. 
HAVE comets originated in the solar system, or do they enter 
it from without? This question has been considered by La- 
place, Proctor, H. A. Newton, and others. The last named 
presents arguments of no little weight in favor of their origin 
in inter-stellar space.* To these arguments I shall attempt no 
reply. On the contrary, I have been disposed to accept them 
as, in the main, valid. For certain comets of short period, 
however, various facts seem to indicate an origin within the 
system. 
(1.) According to M. Lehmann-Filhés the eccentricity of 
the third comet of 1884, before its last close approach to 
Jupiter, was only 0°2787.¢ This is exceeded by that of twelve 
known minor planets. Its period before this great perturbation 
was about 3619 days, and its mean distance 4611. It was then 
an asteroid, too rernote to be seen, even in perihelion. Its pe- 
riod was very nearly commensurable with that of Jupiter; six 
of the one being very nearly equal to five of the other. Ac- 
cording to Hind and Krueger the great transformation of its 
orbit by Jupiter’s influence occurred in May, 1875. Its pres- 
ent period is about 6$ years. It was discovered by M. Wolf 
at Heidelberg, September 17, 1884. Its history indicates an 
origin in the zone of asteroids, 
(2.) The second comet of 1867.—This body was discovered by 
M. Tempel on the third of ‘April. Its perihelion distance is 
2073 ; its aphelion 4:8973; so that its entire path, like those of 
the asteroids, is included between the orbits of Mars and 
Jupiter. The eccentricity of this comet at its successive re- 
turns has been as follows: 
Date of Return. Kecentricity. 
1867 ; : j : 0°5092 
1873 : : 2 : 0°4625 
1879 ; F : 7 0°4624 
1885 ; : : . 0°4051 
The last is nearly identical with the eccentricity of Aithra, 
the 132d asteroid, (0°38.) The period, inclination, and longi- 
tude of the ascending node are approximately the same with 
those of Sylvia, the 87th minor planet. 
This comet may be regarded as an asteroid whose elements 
have been considerably modified by perturbation. 
Other comets furnish suggestive facts which bear upon the 
same question; but their discussion must await the develop- 
ment of additional data. 
* This Journ., Sept. 1878. + Annuaire, 1886. 
