C 2+7 ] 
terreftrial fphere, rather than the apparent diameter at 
the horizon, which is not affedted by refra&ion. 
Without this, if the one was confounded with the 
other, an error would arife for the latitude of Paris 
from o'', 25 to o /7 ,32. 
§ 2. Let us keep the fame denominations of P, p y 
and A, and call D the apparent femi-diameter of the 
moon at the centre of the fphere, and d= the apparent 
femi-diameter of the moon at the zenith diftance 
=A. We fhail have fin. A : fin. A-\-p : : tang. D : 
tang. d, or if one will, fin. A: fin. A-{-p : : D : d: the 
error not exceeding an 100th part of a fecond. 
§3. We had above fin. p~{m. P fin. A+p. 
Hence fin. P fin. A : fin./> : : (tang. D:tang. d ) : : D:d, 
or becaufe fin. 
cof. p fin. P fin. A 
$ 1 — fin. P cof. A * 
I — fin. P cof. 
A: cof. p\\ D, d, and d — P co , ; A * 
§ 4. Mr. Euler, in the Memoirs of the Academy 
of Berlin,’ 1747* pag. 175, makes this fame value = 
— — r, and according to him, V— D. M = fin. P 
1 — p fin. hi* ® 
fin. h — cof. A \py from whence it appears, that the 
true value of the apparent diameter of the moon, is 
not more difficult to be computed than the approxi- 
mated one of Mr. Euler, the exadt and geometrical for- 
mula being tang, d — ^ j- and that of Mr. 
Fnle r d — — — ; for in both, the values 
1 — fin. P cof. A + p 
of D, A and f mull be employed. 
§ 5 - 
