of Halley's Comet at its last Appearance. 37 



declination only half its value. May 1st, five other stars were 

 observed, besides the comet; the positions of the comet re- 

 sulting from them differ in rigtit ascension as much as 2', and 

 in declination as much as 3' from each other. However, I have, 

 like Maraldi himself, taken the mean of all. The subsequent 

 observations seem to be much better than one would suppose 

 from this specimen. 



3. Cassini published his observations, with all the necessary 

 details, in the Mem. de VAcad. An 1767. Both he and Ma- 

 raldi complain of the great difficulty of observing, from the 

 ill-defined limb of the comet ; on which account they used to 

 make several comparisons with the same fixed star in one 

 night, and take the mean from the most certain ones. He states 

 his time only to minutes, nor does he say whether we are to 

 understand mean or apparent time. But as all other observers 

 state the true time, as Cassini himself does with the comet of 

 1767, the observations of which are contained in the same 

 volume of the Parisian Memoirs; as, moreover, the first of 

 his observations with regard to the compared star and the ob- 

 served differences of right ascension and declination exactly 

 agrees with one of Maraldi's observations on May 1st, and the 

 times of observation agree even to seconds, so that both must 

 allude to the same observation, I thought myself justified in 

 assuming that the time of observ;ition stated by Cassini, is, 

 like that of Maraldi, the true time. He also mentions, be- 

 sides the position of the compared star, and the differences of 

 right ascension and declination of the comet, the places of the 

 latter as deduced from them ; a practice which made it possible 

 to discover and correct some errors of the press. Only the 

 declination of May 22nd remained uncertain by one minute, 

 and has consequently been omitted. The time of the observa- 

 tion of May 28th is not stated. I have therefore taken the 

 mean between the extreme data of the days immediately pre- 

 ceding this, which, considering the very slow motion of the 

 comet at this period, will be sufficient. 



4. As Bradley's observations have never been published 

 before, it will, perhaps, be allowable to introduce them here. 

 They are exactly copied from the MS. transmitted to Professor 

 Bessel. 



[^The author here gives Bradley" s Observations, for isohich the 

 reader is referred to the Astronomische Nachrichten.] 



To this table Prof. Bessel has added the following note : 

 " Whatever is underlined is of Bradley's own hand; and the 

 remainder was probably written by his nephew, John Bradley. 

 Dr. lligaud writes, ihat regular observations were made at 

 Sherburne Castle, I* or 15 miles from Oxford, by direction 



of 



