3* 6 -Dr. Herscmel’s Astronomical Observations 
solidation which will no longer permit the internal penetration 
of light, and thus a planetary appearance must in the end be 
the consequence ; for planets are solid opaque bodies, shining 
only by superficial light, whether it be innate or reflected. 
From the size of the nebulae as we see them at present, we 
cannot form an idea of the original bulk of the nebulous matter 
they contain ; but let us admit, for the sake of computation, that 
the nebulosity of the above described nebula IV. 55, when it 
was in a state of diffusion, took up a space of lo'in every 
cubical direction of its expansion ; then, as we now see it col- 
lected into a globular compass of less than one minute, it must 
of course be more than nineteen hundred times denser than it 
was in its original state. This proportion of density is more 
than double that of water to air. 
With regard to planetary disks, which have bright central 
points, we may surmise that their original diffused nebulosity 
was more unequally scattered, and that they passed through 
the different stages of extended nebulae, gradually acquiring 
a nucleus, chevelure, and branches. For in nebulae of this 
construction, the consolidation of a nucleus is already much 
advanced at the time when a considerable quantity of nebu- 
lous matter, on account of its greater central distance, re- 
mains still unformed in the branches; and if the condensa- 
tion of the nucleus should keep the lead, it will come to a 
state of great solidity and maximum of brightness by the time 
that the rest of the nebulosity is drawn into a planetary ap- 
pearance.. 
