109 



Art. XIII. ASTRONOMICAL AND NAUTICAL 

 COLLECTIONS. 



No. XXI. 



i. Remarks on the determination of the LoNGiTUDE,yro7» Obser* 

 rations of the Moons Right Ascension, By Thomas Henderson, 

 Esq, 



In the Connaissance des Terns, for 1825, p. 345, M. Bouvard gives 

 a formula for the computation of the diiFerence of longitude be- 

 tween two places, by means of the observed motion of the moon 

 iQ right ascension, during the interval elapsed in passing from the 

 one meridian to the other. It is this, 



= «r(^^°+;'-^) 



where a represents the observed motion of the moon in right as- 

 cension expressed in sidereal time, r the ratio of sidereal to mean 

 time, tn the mean horary motion of the sun, h the horary motion of 

 the moon in right ascension for one hour mean time, and d the 

 difference of longitude required. 



It appears to me that this formula is erroneous, in so far as r 

 is introduced ; and that it ought to have been 



Which may be demonstrated thus: — 



From the observed right ascension of the moon upon the meri- 

 dian of the first place, calculate the mean time at Greenwich of 

 the observation, and the right ascension of the meridian at Green- 

 wich, by adding to the mean time there the sun's mean longitude 

 at this time. The difference between the right ascension of the 

 meridian at Greenwich, and the right ascension of the meridian at 

 the place of observation, (being the same as the observed right 



