1 
A CATALOGUE OF OBSERVATIONS OF LUMINOUS METEORS. 413 
regarding the concentration of an original nebulous matter* into celestial 
bodies of the various forms and characters visible in the universe, when ap- 
plied to the case of shooting-stars, has brought to light the following con- 
clusions, viz. (1) the production of meteoric streams, (2) the affinity of their 
orbits with those of comets, (3) the presence of comets in them forming an in- 
tegrant part of certain meteor-currents. Many important considerations are 
here, accordingly, introduced. 
In the first place, in the opinion of Faye, meteor-currents may arise from 
the dispersion of the nucleus of comets, which Laplace regarded as small 
portions of the nebulous matter of Herschel overtaken by the sun’s attraction 
in spacet. Meteoric clouds Professor Schiaparelli considers to be of exactly 
the same origin but at the same time of greater extent and tenuity than the 
nuclei of comets, and, finally, that they assume the form of meteoric currents 
when (under the influence of the sun’s attraction) they approach the interior 
portion of the solar system. A few general calculations, at the outset, 
are therefore given, to show what relations the dimensions and the du- 
ration of the perihelion passage of the meteoric currents must bear to the 
original extent and distance of the meteoric clouds, on the supposition that 
the mutual attractions of their particles may be neglected. It may, how- 
ever, be shown that if two gravitating spheres, composed of uncohering par- 
ticles, are placed close together, one of them incomparably smaller than the 
other, and revolving round it in an orbit, the attraction of the larger sphere 
will overcome the mutual attraction, and distribute the particles of the smaller 
sphere in the form of a current along its orbit, unless the smaller sphere has 
at least twice the density of the larger one. Supposing the sun’s mass to be 
extended into a sphere of the same radius as the earth’s orbit, it will contain 
2:3 grains weight of matter per cubic yard, which is the density of common 
air at a barometric pressure of about 1, part of an inch (00337 in.) 
of mercury. Twice this density is therefore the least density which a come- 
tary body can have at the earth’s distance from the sun, without undergoing 
gradual deformation by the sun’s attraction into an elongated current. In 
the case of meteoric clouds, which are of extreme tenuity, and have no nu- 
cleus, or only such a small nucleus as the November meteors appear to pos- 
sess in Tempel’s comet, the deformation is certain to take place; but in the 
case of certain comets which appear to possess a nucleus of considerable 
density, their parts may remain connected throughout their perihelion pas- 
sage, or at least will not be permanently separated until they approach within 
a certain distance from the sun. The first steps of deformation of the group 
of the November meteors may accordingly not have commenced until they 
were deflected into their present orbit by the forcible attraction of one of the 
superior planets ; and a part of the same group appears still to retain its ori- 
ginal compact form in the gaseous mass of Tempel’s comett. 
In this view, comets and meteoric showers are portions of the nebulous 
matter in space in two different states of condensation (comets or meteors), 
which may either arise together or apart, according to the tenuity of the mat- 
* “ Astronomical Observations relating to the Construction of the Heavens,” Phil, 
Trans. for 1811. 
+ The occasional smallness of comets may be gathered from a singular observation by 
Jahn (Astronomische Nachrichten, vol. xxiii. p. 237) of a comet with three tails, which, on 
the 3rd of July, 1845, described an are of nearly 40° in about 26 minutes, during which 
it remained visible. This comet must have passed very close to the earth, and must have 
been of very small dimensions. (Schiaparelli’s Memoir, p. 106.) 
{ The nucleus of this comet was shown to consist of ignited gas, with the spectroscope, 
by Mr. Huggins (Proceedings of the Royal Society, vol. xv. p. 6, Jan. 11, 1866). 
