relating to the Construction of the Heavens . 
307 
23. Of Nebulce that are suddenly much brighter in the middle . 
From the third degree of visible condensation, I have in the 
21st article intimated, that the length of the time of the action 
of the attracting principle, would explain the observed gradual 
accumulation of the nebulous matter. In the following eigh- 
teen nebulae we may see a still more advanced compression 
of it, amounting almost to the appearance of a nucleus.* 
II. 814 is “ A small faint nebula, very suddenly much 
44 brighter in the middle/’ 
I. 39 is “ A very bright nebula, extended from south-pre- 
ceding to north-following, about 4' or f long, and 3' broad ; 
it is much brighter in the middle, but the brightness breaks off 
abruptly, so as almost to resemble a nucleus.” Fig. 23. 
I. 2 36 is “ A very bright pretty large nebula of an irregular 
“figure; it is suddenly much brighter in the middle.” 
Fig. 24. 
I. 99 is 44 A very bright, small, round nebulae ; it is very 
44 suddenly much brighter in the middle.” Fig. 25. 
From the appearance of these nebulae, we see plainly that 
a progressive concentration of the nebulous matter has an 
existence ; it is also remarkable that the condensation in long 
nebulae inclines towards the shape of a nucleus, as well as in 
• See One nebula of unascertained, figure , suddenly much brighter in the middle. 
II. 814. 
Seven extended nebulce, suddenly much brighter in the middle. I. 39, 91, 96, 200, 
II. 183, 505. Connoiss. 66. 
Two i nebulce of an irregular figure, suddenly much brighter in the middle. I. 256. 
II. 521. 
Eight round or nearly round nebula, suddenly much brighter in the middle. I. 991* 
138. II. 410, 413, 698. III. 251, 685. Connoiss. 54. 
R r 2 
