414 REPORT—1868. 
ter which produced them. Such differences are observed in the nebulw, of 
which some are resolvable and others not resolvable in the telescope ; and a 
similar distinction is shown to exist in the nebulz by the spectroscope. 
Comets with two or more nuclei, sometimes resembling a congeries of 
stars, have not uncommonly been observed. Of such observations several 
descriptions, illustrated by engravings (see fig. 1), are cited, for the details of 
which the reader is referred to the original memoir (p. 94-101). The ex- 
traordinary comet of 1652, witnessed by Hevelius (fig. 2), consisted of a 
disk of pale light of the apparent diameter of the full moon, with hardly any 
perceptible tail, and, in the telescope, it appeared filled with points of light. 
A large proportion of shooting-stars are, in fact, telescopic ; and a display of 
diffused light is said sometimes to accompany a meteoric shower. 
Fig. 1. 
Dec .20. =F wy 
SS 
a 
= — 
at =m 
1. Nucleus of the large comet of the year 1618, observed with a telescope by Cysatus. 
2. Comet of the year 1652, as observed and drawn, on the 27th of December, by Hevelius. 
How, then, can the tAn of Anaxagoras, or the nebulous matter of Herschel 
become condensed into bodies of such various characters, except it be from 
a state of highly heated vapour, gradually undergoing a process of cooling 
and condensing of its parts? Groups of more or less comminuted particles, 
or compact nuclei would thus result, according as the original form of the 
heated cloud was that of a filament or thin extended disk, or a sphere. Not 
only the various features of star-showers and comets, but even the mine- 
ralogical structure of aérolites, whose crystals appear to have been deposited 
from a heated vapour, to have been broken up, and to have, in some cases, 
again undergone metamorphism by heat, before they were finally consoli- 
dated, appear to be explained on this:supposition. The theory of Faye, that 
they are developed from the nuclei, and of Secchi, that they are the remnants 
of the tails, and of Erman, that they are particles detached from comets by a 
resisting medium, are not so immediately referable to the known laws of 
gravitation as the hypothesis that all classes of luminous meteors, like comets 
themselves, are drawn towards the sun by its attraction from the regions of 
intrastellar space, which the telescope declares to be empty, but which, in 
all probability, are strewed with cosmical clouds, containing in one order of 
phenomena both meteoroids and comets. 
The ninth and tenth chapters of the memoir conclude with some further 
notices and reviews of recent opinions regarding the connexion between comets 
and shooting-stars, and demonstrations concerning a certain luminosity of 
