170 Prof. D. Kirkwood on the Nebular Hypothesis. 
temperature as would be fitted to permit their oceanic matter 
permanently to descend and remain upon the surface, would be 
vastly longer than in the case of such a comparatively small planet as 
earth,” 
Thus, in accordance with the nebular hypothesis, it would 
seem that Jupiter and Saturn, on account of their vast dimen- 
sions, still retain so much of their primitive heat as to produce 
the vaporous envelopes by which they are surrounded. 
by Mr. A. D. Wackerbarth, as follows: ‘Suppose a nebula 
such as that from which the earth, sun, and planets, are suppos- 
bly be composed of elements more or less the same as those 
whereof our own planet is furmed.* Some, indeed, of the lat- 
ter we might suppose wanting, and others present which we 
possess not here; but on the whole, let us suppose that 
e ¢ 
would thus form an immense spheroid of nebulous matter Te- 
volving round its own minor axis; or rather, if that matter were 
not quite homogeneously distributed, on an axis passing throug 
its centre of gravity. We may suppose or not as we please, that 
this nebula has a nucleus, as many nebula appear to have, au 
many not to have, any such portion; but in the former case we 
nebula, thus composed, may wander a longer or shorter period 
in space peacefully ; but now let us suppose a disturbance such 
any cause, which would bring them and the oxygen into contact, 
would cause fearful explosions, and set the whole nebula 2 
* It is a remarkable fact that no new elements have been found in meteori¢ 
stones, which are now d 
sphere, a en form 2 
from vaporous rings describing their orbits round the central body ?” (Cosmos, ra 
i, p. 120.) Mr. Wackerbarth extends this hypothesis in regard to the identity of 
to stellar systems, 
f 
; 
