3 P9 
relating to the Construction of the Heavens, 
f I. 151 is “ A considerably bright and considerably large* 
« round cometic nebula; it is very gradually much brighter 
“ in the middle, with a nucleus in the center.” Fig. 26. 
From the description of these nebulae, we find that an ac- 
tual nucleus has been formed in the attracting center ; and 
that consequently a certain degree of consolidation of the 
nebulous matter is highly probable ; for, although the quality 
of shining only points out the existence of something that is 
luminous, yet from analogy we have reason to conclude that 
certain material substances must be present to produce the 
light we perceive ; and that they must be opaque, may be 
inferred from every thing we know about shining substances. 
25. Of Nebulce that have a Nucleus* 
It may be expected that some considerable change will 
take place in the appearance of a nebula after it has come to 
a certain degree of continued gradual condensation. We are 
as yet so little acquainted with the nature and distribution of 
this matter, that an application of mathematical calculations* 
founded on the attraction of gravitation, for want of data, can- 
not be applied in order to suggest to us what appearance 
might next be expected ; I shall therefore proceed in a re- 
gular manner to give the observations, which shew what 
these appearances are, without entering into any theoretical 
discussions. 
In the following two assortments v/e have forty nebulae.* 
* See Twenty- seven extended nebalce, with a nucleus. I. 43, 77, 126, 156, 170, 
180, 208, 224., 240, 250, 255, 270, 280, 281. II. 238, 460, 739, 768,' 796, 8465, 
849, 891. V. 18, 24, 48. Connuiss. 63, 101. 
Thirteen round or nearly round nebulce, with a nucleus. I. 107,133, 139, 152, I 6 j 3 
203, 225, II. 99, 501, 746, 754. HI. 178. Connoiss. 90, 
