with Remarks on the Construction of its diffemit Parts. 337 
In its approach to a perihelion, a comet becomes exposed 
to the action of the solar rays, which, we know, are capable 
of producing light, heat, and chemical effects. That their in- 
fluence on the present comet has caused an expansion, and 
decomposition of the cometic matter, we have experienced in 
the growing condition of the tail and shining quality of its 
light, which seems to be of a phosphoric nature. The way 
by which these effects have .been produced may be supposed 
to be as follows. 
The matter contained in the head of the comet would be 
dilated by the action of the sun, but chiefly in that hemisphere 
of it which is immediately exposed to the solar influence ; and 
being more increased in this direction than on the opposite 
side, it would become eccentric, when referred to the situation 
of the body of the comet ; but as the head is what draws our 
greatest attention, on account of its brightness, the little pla- 
netary body would appear to be in the eccentric situation in 
which we have seen it. 
Now, as from observed phenomena, we have good reason to 
believe the comet to be surrounded by a very extensive, trans- 
parent, elastic atmosphere ; the nebulous matter, which pro- 
bably, when the comet is at a distance from the perihelion, is 
gathered about the head in a spherical form, would on its 
approach to the sun be greatly rarefied, and rise in the cometic 
atmosphere till it came to a certain level, where it could re- 
main suspended, for some time, exposed to the continued 
action of the sun. 
In this situation we have had an opportunity of seeing the 
transparent atmosphere, which, but for the suspension of the 
nebulous matter, we might never have discovered; and 
mdcccxii. T 
