THE NEBULAR HYPOTHESIS: ITS PRESENT CONDITION. 
27 
with uneven gradations of intensity. This is very much what 
would be expected if the spectrum were really one of numerous 
bright lines, nor is it a singular instance. Several other nebulae 
have given rise to strong suspicions of a similar constitution ; 
and no theory, so far as I am aware, has hitherto been ad- 
vanced in explanation of these appearances. I need not point 
out that, if this supposition is correct, a state of things arises in 
which the nebular hypothesis in its later form will again apply, 
with the addition only that the gases of the nebulae are in a 
much more complicated condition than was formerly supposed 
to be the case. 
It is to be remarked, that the number of comets which would 
be attracted to a nebula would increase in proportion as its 
mass increased with each succeeding capture, so that its de- 
velopment would proceed art an accelerated rate until a certain 
point was reached, when comparatively little of the gaseous ele- 
ments remained. The comets would then describe their orbits 
around the newly-formed sun, and would leave only their 
smaller or outlying meteorites to swell its mass. But even these 
would greatly tend to compensate for the dissipation of heat by 
radiation, and would much retard the cooling process — a state of 
things that will continue to exist even in a perfectly formed 
system such as our own. I am thus led to regard the meteoric 
theory of the supply of solar heat as a part of the modified ne- 
bular hypothesis which I have suggested. If our sun is a 
nebulous star, surrounded by a far-extending atmosphere, in 
which are revolving a large number of meteoric bodies, visible 
possibly to us as the Zodiacal Light, the materials for keeping up 
a constant or nearly constant temperature for a considerable 
length of time are at hand, and every succeeding comet will add 
some to the number of those meteors which, unlike it, are un- 
able to make their final escape, and pursue their orbits with 
scarcely diminished velocity. The smaller meteors in a stream, 
as presenting relatively a larger surface, will be more retarded 
than the larger, and will more rapidly fall upon the solar sur- 
face — so rapidly, indeed, that it does not seem unlikely that the 
universally held belief in the increased solar heat during years 
noted for large comets may have a sound foundation. Such a 
possibility is sufficient to invest the movements of comets with 
great practical interest, and the various circumstances pro- 
ducing the increased heat of such seasons must give rise to 
important investigations. Thus we should come to look upon 
the nearness of approach of a comet in perihelion as an essential 
element in such a discussion, and perhaps also the material 
composition of the comet itself. It has been suggested, with 
much show of reason, that the larger and nearer planets when 
in perihelion simultaneously have a considerable effect upon 
the solar surface by producing spots, &c., and these again, in 
