BSO Obfervations on 



There is no danger, that the late comet will ever" 

 flrike the earth ; unlefs its orbit fhould, hereafter, be 

 materially changed. Its leaft diftance, in the prefent 

 inftance was more than an hundred million miles. This 

 was about the middle of October. Its neareft approach 

 to the orbit of the earth, was on the 1 1th of July, about 

 40 million miles. It can never come much nearer than 

 this, without a change in the pofition or figure of its 

 orbit. Its rate of motion, when neareft the fun, was 

 95,000 miles in an hour. This is a velocity, 120 times 

 greater than that of found, or a cannon ball. 



For the purpofe of determining, if practicable, the 

 si%e of the comet, I viewed it feveral times, through a 

 three feet refleaing telefcope, with a magnifying pow- 

 ^r of 140. But I was unable to perceive any nucleus, 

 with a dilk fufficiently defined, to admit of meafur- 

 ing its diameter. This will not appear furprifing, when 

 it is coniidered, that out of 15 or 20 comets, which 

 Dr. Herfchel has had an opportunity of obferving, there 

 were only two or three, on which he was able to difco- 

 ver any regular diik, even with the very powerful 

 telefcopes in his poifeffion. For want of a proper re- 

 gard to the diftin£tion between the different parts of a 

 €omet ; no great dependence is to be placed, upon the 

 accounts given us, of the iize of thofe, which were 

 formerly feen. They have been frequently reprefent- 

 ed, as larger than any of the planets ; and, in fome 

 inftances, as appearing nearly equal to the fun and 

 moon. Thefe ftatements may be true, if they are 

 meant to refer to the vjhole of the luminous fpot, or 

 body of light, which is perceived, by the naked eye. 

 But this, in many cafes at leaft, confifts of three parts 

 -—the nucleus, the head, and the coma.^ The nucleus 

 appears to be a compact fpherical body, with a circum- 

 ference regularly defined, like a planet. The head, is. 

 a body of denfe light, which, like an atmofphere, fiir- 

 rounds the nucleus. The coma, is a fpace occupied by 

 a fainter light, extending confiderably farther round,, 

 than the head. All thefe may be fo blended, to the, 

 view of the naked eye, as to appear to conftitute but 



