14a Dr. Herschel's Observations of a Comet , 
rendered probable from our knowing as yet, with certainty, the 
return of only one comet among the great number that have 
been observed. 
Since then, from what has been said, it is proved that the 
influence of the sun upon our present comet has been beyond 
all comparison greater than it was upon that of 1807; and 
since we cannot suppose our sun to have altered so much in 
its radiance as to be the cause of the difference ; have we not 
reason to suppose that the matter of the present comet has 
either very seldom, or never before passed through some 
perihelion by which it could have been so much condensed as 
the preceding comet ? Hence may we not surmise that the 
comet of 1807 was more advanced in maturity than the pre- 
sent one; that is to say, that it was comparatively a much 
older comet. 
Should the idea of age be rejected, we may indeed have re- 
course to another supposition, namely, that the present comet, 
since the time of some former perihelion passage, may have 
acquired an additional quantity ( if I may so call it ) of unpen - 
helioned matter, by moving in a parabolical direction through 
the immensity of space, and passing through extensive strata 
of nebulosity ; and that a small comet, having already some 
solidity in its nucleus, should carry off a portion of such matter, 
cannot be improbable. Nay, from the complete resemblance 
of many comets to a number of nebulae I have seen, I think it 
not unlikely that the matter they contain is originally nebu- 
lous. It may therefore possibly happen that some of the 
nebulae, in which this matter is already in a high state of con- 
densation, may be drawn towards the nearest celestial body 
of the nature of our sun ; and after their first perihelion pas- 
