264 i-HILOSOPHlCAL TRANSACTIONS, [aNNO IjfiS. 



The impatience of astronomers, and their desire to prepare for verifying this 

 prediction of Dr. Halley, had put them on inquiring for several years in what 

 part of the heavens this comet was likely to appear; hut, being ignorant of the 

 exact time of its return, they could not determine the spot where it might be 

 expected to be seen, but by making various n suppositions as to the time of its 

 perihelium. This Mr. Dirck of Klinkenberg, a famous astronomer, had at- 

 tempted 7 or 8 years before, having taken the pains to calculate the principal 

 points of 14 different tracks, which the comet was to take, on as many different 

 suppositions relating to its passage through its perihelium, almost from month 

 to month, from the IQth of June 1757 to the 15th of May 1758. Messrs. 

 Pingre and de la Lande proceeded much in the same manner, in the calculations 

 they published in the Memoirs of Trevoux for April 1759, 1st and 2d parts, 

 with this difference, that the latter in their suppositions had taken narrower 

 limits, and nearer to Mr. Clairaut's determination, who had fixed the return of 

 this comet to the middle of April. 



Mr. de L'Isle, being curious of seeing the comet on its first return, as soon 

 as it could be discovered by means of telescopes, before it was visible to the 

 naked eye, thought he must proceed in a different manner from what othei* 

 astronomers had done, to find out in what part of the heavens it must be looked 

 for. He considered that it was not necessary to know its place throughout its 

 whole course, but only at the first moment of its appearance, because, having 

 once found it out, it would be an easy matter afterwards to trace it through its 

 whole progress by observation and calculation. A full description of this method 

 is found in an ample memoir concerning this comet, which Mr. M. laid before 

 the Royal Academy of Sciences at Paris, with a northern hemisphere, by means 

 of which he was enabled to look for this comet in the very place of the sky, 

 where it ought to appear, and it was by the help of this planisphere that he dis- 

 covered the comet from the Marine Observatory at Paris on the 21st of January 

 in the evening, after searching for it 2 years successively whenever the sky 

 would permit. After this first discovery of the comet on the 21st of January 

 1759, Mr. M. continued to watch it daily, and made observations of it every 

 day, either night or morning, that it could be seen for the weather or its own 

 situation; till the 3d of June following, when he saw it for the last time. 



The fallowing are the elements of the comet, as computed by Messrs. de la 

 Caille, Maraldi, and De Lalande. 



Mr. de la Caille. M. Maraldi. M. de la Lande. 



Place of the ascending node 1' 23° 49' 0" I' 23° 49' 41" V 23° 45' 35" 



Inclination of tlie orbit 17 39 17 35 20 17 40 14 



Place of the Perihelion 10 3 1(5 10 3 16 20 10 3 8 10 



Logarithm of the distance at the perihelion 9.766"039 9.t66\15 9.76?0848 



Time of the perihelion • March 12. at 13" 41' at 12" 57' 36" at 13* 59' 24" 



Mean time, at the meridian of Paris. The motion of the comet was retrograde. 



