VOL. LIV.] PHILOSOPHICAL TRANSACTIONS. H^ 



Below are the elements of the theory of this comet, which M. Pingre deduced 

 from M. Messier's first observations. 



The ascendmg node $| ". 3' 29° 20' 6" 



Inclination 33 54 1 Q 



Place of perihelium 16 1 1 48 



Logarithm of the perihelium distance .... 9.751415. 



Passage by the perihelium Feb. 12, at lO'' 29"" mean time in the meridian of 

 Paris. The motion retrograde. 



XXFIII. A Supiilement to Mons. Pingre s* Memoir on the Suns Parallax. 

 Translated from the French by M. Maty, M.D., F.R.S. p. 152. 

 Mr. Pingre was anxious to determine which of the observations, viz. that of 

 Messrs. Mason and Dixon made at the Cape of Good Hope, or that which was 

 made at the Island Rodriguez by Mr. Thuillier and him, deserved the prefer- 

 ence. The first reduces the sun's parallax to S% at most, whereas the latter 

 increases it to near IQf : the difference is too considerable not to deserve an in- 

 quiry into its aiuses. In the Phil. Trans, for 176l-|- are two observations, which 

 would be decisive, if time and other circumstances had permitted them to be 

 made with sufficient accuracy. Mr. Maskelyne observed at the island of St. 

 Helena, situated at 15° 55' south latitude, and according to Dr. Halley at SS"" 

 17' of time west of the Observatory at Paris. But this determination of the 

 longitude does not seem sufficiently exact. On comparing many observations of 

 Jupiter's satellites immersions and emersions, made at the island of St. Helena 

 by Mr. Maskelyne, with the corresponding ones made at Paris at the Marine 

 Observatory by Mr. Messier, he has only found 31™ 56' for the difference of 

 longitude between the two places ; and as the Marine Observatory is 2* east of 

 the Royal Observatorj', we may conclude that the place where Mr. Maskelyne 

 observed is only at 31™ 54** west of the Royal Observatory. Mr. Maskelyne's 

 observation being compared with that of Tobolsk, would give 1 \" for the hori- 

 zontal parallax, which is a little too much. Let the distance determined by 

 Mr. Maskelyne be only diminished by 2% and his observation will perfectly agree 



• Alexander Guy Pingre was born at Paris in 1711 ; and he died in 1796; consequently at 85 

 years of age. He applied with great assiduity to scientific pursuits, and became librarian of St. Gene- 

 vieve at Paris. In 176'0 he was sent to the South Sea to observe the approaching transit of Venus 

 over the sun's disk. He was afterwards enoployed in proving the going of the time-pieces of M. 

 Leroy. He was first admitted a member of the Academy of Sciences ; and afterwards of the National 

 Institute. M. Pingro's works chiefly are: 1. State of the Heavens from 1754 to 1757. 2. Me- 

 moirs of Discoveries made in the South Seas, 4to. 3- Historical and Theoretical Treatise on Co- 

 mets, 2 vols. 4to. 4. Translation of Manilius's Astronomies, 8vo. 5. History of Astronomy in the 

 17th Century. 



t See p. 557 and 5^6 of vol. xi. 



