comet of 1807 — 8. 369 



This evening I observed an emersion of the 1st satellite of 

 Jupiter, with a six feet Gregorian reflector, power 128, at 

 Si> 27' 5 Si" mean time; a fine observation; the sky was very 

 serene: from the darting of the first ray from the satellite, it 

 seemed a mere point of light for 15 seconds of time; perhaps 

 with telescopes in general use the satellite might have remained 

 invisible during those 15 seconds, which would affect the lon- 

 gitude resulting from the observation; from the above, the lon- 

 gitude deduced is 6" 5' 55 1" west of Greenwich. 



The following are my own observations: — 



1807, October 2d. The reflecting telescope, power 128, be- 

 ing directed to the comet, shewed the nucleus and coma with 

 tolerable distinctness; the idea produced in the mind of the 

 observer,, was that of a round body in combustion, which had 

 produced so much smoke as to obscure the nucleus; the smoke 

 seemed to be emitted in every direction; but, as if it met on one 

 side with a gentle current of air, the smoke seemed to be re- 

 pelled and bent round the nucleus, escaping on the opposite 

 side, in the direction of the tail. To the naked eye, the comet 

 could not be seen earlier in the evening than a star of the se- 

 cond or third magnitude, although its disk was considerably larg- 

 er; with the telescope, the nucleus did not seem to be much more 

 than one third, certainly not- one half of the planet Mars, which 

 had been lately observed. The Coma seemed to be at least ten 

 times the magnitude of the nucleus; an imperfect measure was 

 taken of the tail, which was about 63' in length. The coma 

 appeared to be, in a certain degree, illuminated from the nucle- 

 us, and the whole was compared by many persons to a distant 

 building on fire. This evening, the following observations were 

 made: — 



hi o i ii 



At 



3d. At 



4th. This evening there was an occultation of the planet 

 Mars by the moon, at 7 h 2' l" mean time: the moon was low, 

 involved in the grosser horizontal atmosphere, and, apparently, 

 almost touching the tops of the forest trees. 



