with Remarks on the Construction of its different Farts. 333 
Of the real Construction of the Comet , and its various Parts. 
Hitherto I have only related the appearances of the several 
parts of the comet, in order to determine their linear extent ; 
but the observations which are now before us, contain facts 
that will allow me also to ascertain the construction of the 
comet and its various parts in their solid dimensions. 
From the laws of gravitation we might be allowed to con- 
clude that the planetary body containing the solid matter of 
the comet must be spherical ; but actual observation will fur- 
nish a more substantial argument; for in no part of the long, 
geocentric path described by the comet, did I see its little disk 
otherwise than round ; whereas it would not have preserved 
this appearance, if its construction were not spherical. 
If what has been said in my last paper, when treating of 
round nebulae, be remembered, the head of the present comet, 
which by observation appeared round like a nebula, cannot 
be supposed to be of any other than a spherical construction. 
With my collection of round nebulae the arguments, however, 
which proved their globular form, rested only, though very 
soundly, upon the doctrine of chances, and the known effects 
of gravitation ; but here, on the contrary, while nebulae re- 
main in their places, the geocentric position of the head of the 
comet has undergone a change amounting to a whole qua- 
drant ; in all which time I have observed it to retain its round- 
ness without any visible alteration ; from which it necessarily 
follows that its form is globular. 
With regard to its transparent cometic atmosphere, we have 
not only the constant observations of its roundness, during 
the abovementioned long period of the comet's motion, to 
