304 Dr. Herschel’s Astronomical Observations 
“ ing very gradually from the center towards the circum- 
“ ferenceT Fig. 18. 
From the account of these nebulas, we find again that all 
what has been said concerning the seat of the forming and 
condensing power of the nebulous matter, is abundantly con- 
firmed by observation. 
I have only to remark that, the exertion of the gravitating 
principle in these nebulas, is in a more advanced state than 
with those of the last article ; and that the same conceptions 
which have already been suggested, namely, the original 
form of the nebulous matter ; its quantity in the seat of the 
attracting principle ; and the length of the time of its action, 
when properly considered, will sufficiently account for the 
present state of these nebulas. 
21. Of Nebula: that are gradually much brighter in the middle. 
The nebulous matter which appears under the various 
forms of the following four assortments, containing two hun- 
dred and two nebulae, assumes now a more condensed aspect, 
than that under which it was seen in either of the two fore- 
going collections ; and thus by its gradually greater compres- 
sion, gives us a still more decisive indication of the central seat 
of attraction.* 
* See Twenty Jive nebulae of unascertained figure, gradually much brighter in the 
middle. I. 73. 121, 127, 140, 155, 181, 287. II. 35, 177, 187, 299, 439, 452, 540, 
653, 658, 669, 686, 694, 795, 828, 855, 871. III. 863. Connoiss. 99. 
Fifty-four extended nebulae, gradually much brighter in the middle . I. 29, 31, 33, 
35’ 3 8 ’ 53’ 5 8 ’ 64, 72, 82, 86, 93, 97, 101, 104, 125, 154, 157, 164, 184, 209, 233, 
2 39’ 2 74’ 2 7»’ 2 77- II- 12, 1 3, 31, 3 7, 182, 212, 231, 282, 318, 416, 431, 463, 
504, 604, 612,626,691,701, 702, 704, 725, 753, 775, 875. III. 179. 198. V. 47. 
Connoiss. 49. 
