282 Dr. Herschel’s Astronomical Observations 
condensed in some places than in others. The idea of con^ 
densation occurs so naturally to us when we see a gradual 
increase of light, that we can hardly find a more intelligible 
mode of expressing ourselves than by calling it condensed. 
The numerous instances that will be given hereafter of nebulae 
that have this kind of condensation, renders it unnecessary to 
refer to more than the following four.* 
The first of these, No. 11 in the first class, is “ A bright 
“ nebula of some extent, although not very large. It is of an 
“ irregular figure, and the greatest brightness lies towards 
“ the middle. The whitishness of this nebula is of the milky 
“ kind/’ See figure 4. 
By attending to the circumstances of the size and figure of 
this nebula, we find that we can account for its greater bright- 
ness towards the middle in the most simple manner by sup- 
posing the nebulous matter of which it is composed to fill an 
irregular kind of solid space, and that it is either a little deeper 
in the brightest place, or that the nebulosity is perhaps a little 
more compressed. It is not necessary for us to determine at 
present to which of these causes the increase of brightness 
may be owing ; at all events it cannot be probable that the 
nebulous matter should have different powers of shining such 
as would be required independent of depth or compression. 
7. Of Nebulce which are brighter in more than one Place. 
It is not an uncommon circumstance that the same nebula 
is brighter in several different places than in the rest of its 
compass. The following six are of this sort.f 
* See I. 1 1, 84. III. 457. IV. 12. 
f See I. 165, 213, 3 6 1 r II. 297, 406. III. 49. 
