j 86 Dr. Maskelyne’s Obfervations on the Latitude 
M. Messier, at the Hotel de Clugny, and reduced to the 
Royal Obfervatory is f 20". The mean of both refults is 
9 / 2$ // . But if greater weight he given to the latter determi- 
nation than to the former in the ratio of 2 to f, on account of 
the feries of M. Messier’s obfervations being the molt com- 
plete, the difference of meridians will be 9 7 23". 
M. du Sejour, in the Memoires of the Royal Academy of 
Sciences for 1771, found 9' 20" , as well from the beginning 
as end of the folar eclipfe of 1769. M. Mechain, the learned 
editor of the Connoiffance des Temps, informs me, that from 
the immernons of Celeno and Maia at the moon’s limb, on 
March 5th laft year, he has found by calculation from M. 
Messier’s obfervations compared with mine 9'' 19^,9 and 
9 / i7 7/ ,9, or by a mean 9' i 8 /7 ,9 ; but, by his own obfervations 
compared in like manner, he makes it a little more than f 20" , 
He regulated his clock by correfponding altitudes ; but M. 
Messier corrected his by a tranfit inftrument, which, how- 
ever, has no meridian mark. For the prefent, I infer, we 
may take the difference of meridians 9' 20", as being within 
a very few feconds of the truth, till fome more occultations of 
fixed flars by the moon, already observed, or hereafter to be 
obferved, in favourable circumftances, and carefully calculated, 
fhall enable us to eftablifh it with the laid exadtnefs. To col- 
lect and calculate fuch obfervations I have not leifure at pre- 
fent ; but the field of calculation is equally open to the cele- 
brated aftronomers of Paris, the obfervations made at this 
place being now publifhed annually. 
The extenfive geometrical operations recommended by the 
late M. Cassini de Thury, and commenced under the direc- 
tion of Major-general Roy, F. R. S. by his exadl meafure of a 
bafe on Hounflow- Heath, may alfo, when completed, deter- 
mine 
I 
