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As a particular instance of this, the wide-spread notion of comets 

 shooting forth their tails, at, or a little before the perihelion passage, 

 and drawing them in again afterwards, so as to be larger at that period 

 of their orbits than at any other, was mentioned ; and in place of 

 which, the author shewed that the comets were at the perihelion, of 

 their smallest size ; the tails becoming then more visible, not from 

 being actually produced at that time, but from being more dense, 

 and illumined by a stronger solar light, as well as being in general 

 seen from a smaller terrestrial distance. 



The author then proceeded to collect together the facts which he 

 thought well made out with regard to comets ; to describe the cor- 

 rections which the apparent, required, to give the true phenomena ; 

 and to detail the various practical methods by which better observa- 

 tions might be procured. 



The so-called established facts mentioned above, were collected in 

 a series of axioms, which are here appended ; as they seem to be 

 worthy of being discussed, and either disproved or assented to, by 

 astronomers. 



Ist, A comet consists of a nucleus, and one or more gaseous en- 

 velopes. 



2rf, The nucleus, if solid and material, is infinitely small. 



3d, The nucleus is excentrically situated in the gaseous body. 



4M, Comets of longest period have the largest bodies. 



5th, Those comets whose orbits have the greatest excentricity, are 

 the most excentrically situated in their envelopes, or, vulgarly, have 

 the longest tails. 



6M, A comet revolves on an axis passing through the nucleus, 

 and at right angles to the major axis of the envelope, in the same 

 period of time that it takes to revolve about the sun ; hence the tail 

 being turned away from the sun in the normal position, is turned 

 away from him in all other parts of the orbit also. 



7th, This axis is not at right angles to the plane of the orbit, 

 but variously inclined in the case of different comets, as witli the 

 planets. 



8th, A quicker rotation round the longer axis of the body also 

 appears to exist. 

 _ 9th, A comet shines by refiected light, and shews a sensible 



; phase. 



lOth, The gaseous envelope is of extreme tenuity, is elastic, and, 



