28 6 Dr. Herschel’s Astronomical Observations 
have given two figures for the same double nebulae. For, 
although the nebulosities of figure b, when seen in the direc- 
tion of the dotted lines will appear to run together, they may 
nevertheless be at some small distance from each other ; but 
the same cause which will bring on a separation of it in figure 
a will also make two distinct nebulas of figure b. 
With regard to their being double nebulae, it may be ob- 
jected that this double appearance may be a deception ; and 
indeed if this were a double star, instead of a double nebula, 
there might be some room for such a surmise. But on two 
accounts the case is very different. In the first place, we have 
not nebulae without number at all distances to which we might 
have recourse, in supposing one to be far behind the other, 
as we have stars behind stars to produce an appearance of 
their being double. In the next ; if what has been said of 
the confined range of the visibility of the nebulous matter be 
recollected, especially where it is so faint as in the double 
nebula which has been described, we cannot harbour an idea 
that the two objects of which it is composed are very far 
asunder. Add to this their great resemblance in size, in faint- 
ness, in nucleus, and in their nebulous appearance ; from all 
which I believe it must be evident that their nebulosity has 
originally belonged to one common stock. 
9 . Of double Nebulce that are not more than izvo Minutes from 
each oilier. 
To add to the probability of the separation of nebulae, we 
ought to have a considerable number of them already sepa- 
