French National Inflltute. l8^ 



C. Lalande re-commenced his calculations; fubftituting 

 for the differences of declinations the obfervation of Mercu- 

 ry's paffage of the meridian, made the fame day by his ne- 

 phew and C. Burckhardt; and by ihefc means found il^ lefs 

 in longitude, and 6" lefs for the latitude, at the moment of 

 the cgrefs. 



He determines the geocentric latitude at the time of con- 

 junction to be ^6-^^', which gives the place of the node 

 I' 16^ o 37", further advanced by 1^46^' than in the tables; 

 and as C. Delambre had found by the paffage of 1799 that 

 this element ought to be increafed by i ', C. Lalande adopts 

 a mean correftion of -f- 1' 23'', which makes the place of 

 the node in i8ji to be 



By comparing this determination with that which he de- 

 duced from the tranfit of 1677, he found for the annual mo- 

 tion of the node 43"98" inftead of 43-3'^, which he had be- 

 fore. 



To afccrtain whether the pofition which he gave to the 

 aphelion of Mercury was exaft, C. Lalande examined again 

 the tranfit obferved by C. Delambre in 1799, taking into ac- 

 count the perturbations calculated by M. Oriani, and the 

 error in the tabhs of the fun, and he found the fame error 

 of 13" as ia that of this year, though the anomalies were 

 very difu'rent. He confcquently thought tiiat this error ought 

 to be afcribed only to the epoch of the mean motions : but 

 after a communication from Dr. Mafkelyne in regard to a 

 correAion of 4-" to be made in the right afcenfions, which 

 he afligned to the pofitions of the principal ftars employed 

 for determining the places of the fun, the error in the tables 

 of Mercury would be reduced to 9", and the epoch of the 

 mean motions of this planet would confcquently be for 1801, 

 5^ 11° 53' 33". 



By diflributing this error to the fecular motion it would be 

 reduced 6", and would become 



a' 14° 4' 4". 



In a word, the tranfit of November 9, this year, has fully 

 confirmed the rcfult which C. Delambre deduced from that 

 of 1799 in regard to the diameter of Mercury. C. Delambre 

 had obtained for this diameter as fcen from the fun 6"^^'; 

 and C. Lalande found 6'3", while in his Aflronomy it was 



C. Meflier communicated to the clafs a particular account 



of his obfervation of the tranfit of Mercury, during which 



he fuccefrncly determined twenty-five pofitions of that planet, 



8 comparing 



