with Remarks on the Construction of its different Parts. 143 
sage round it proceed, in a parabolic direction, towards some 
other similar body ; and passing successively from one to an- 
other, may come into the regions of our sun, where at last we 
perceive them transformed into comets. 
The brilliant appearance of our small comet may therefore 
be ascribed either to its having but lately emerged from a ne- 
bulous condition, or to having carried off some of the nebulous 
matter, situated in the far extended branch of its parabolic 
motion. The first of these cases will lead us to conceive how 
planetary bodies may begin to have an existence; and the 
second, how they may increase and, as it were, grow up to 
maturity. For if the accession of fresh nebulous matter can 
be admitted to happen once, what hinders us from believing a 
repetition of it probable ? and in the case of parabolic motions, 
the passage of a comet through immense regions of such matter 
is unavoidable. 
Slough, near Windsor, 
Dec. 16 , 18 1 s. 
WM. HERSCHEL, 
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