go 6 Dr. Herschel's Astronomical Observations 
brighter, there appears to be some foundation for supposing 
rather that this greater effect is produced by a longer time of 
the action of the attractive principle, than that it should arise 
merely from an original more favourable expansion of the 
nebulous matter. 
22. Of Nebula that have a Cometic appearance. 
Among the numerous nebulae I have seen, there are many 
that have the appearance of telescopic comets. The following 
are of that sort.* 
1. 4 is “ A prett}^ large cometic nebula of considerable 
“ brightness ; it is much brighter in the middle, and the very 
“ faint chevelure is pretty extensive/' Fig. 22. 
By the appellation of cometic, it was my intention to ex- 
press a gradual and strong increase of brightness towards the 
center of a nebulous object of a round figure ; having also a 
faint chevelure or coma of some extent, beyond the faintest 
part of the light, gradually decreasing from the center. 
It seems that this species of nebulae contains a somewhat 
greater degree of condensation than that of the round nebulae 
of the last article, and might perhaps not very improperly 
have been included in their number. Their great resemblance 
to telescopic comets, however, is very apt to suggest the idea, 
that possibly such small telescopic comets as often visit our 
neighbourhood may be composed of nebulous matter, or may 
in fact be such highly condensed nebulae. 
* See Seventeen cometic nebulae. I. 3, 4, 34, 217. II. 6 , 15, 33, 59, 104, 153, 154, 
241, 315, 4040 III. 5, 21. Comoiss. 95. 
