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XXIX. *TbeGry of the Parallaxes of Altitude 
for the Sphere , by Mr. F. Mallet, Profejfor 
and AJlronomer at Upfal \ Pranfated from 
the French by M. Maty, M. D. R. S. Sec . 
Upfal, October 25, 1766. 
Read Nov. 20, § i . ’JT ET P be = the moon’s hori- 
J j zontal parallax, or 1 to fin. P, 
as the moon’s diftance to the radius of the terreftrial 
lphere, on which the fpedtator is fuppofed to be placed. 
Let A he the diftance of the moon from the zenith, 
and p the parallax of altitude for the fame diftance. 
The aftronomers ufually compute the value of p in the 
following manner: let fin. p=:fin. P. Sin. A, and 
p f being found by the tables of logarithmic fines, fin. 
P. fin. A yp' is found in like manner, p" 
being afliimed for the true parallax, which is not 
accurate. 
§ 2. In order to fhew this, I have given another 
method of computing the parallax of altitude, as 
exactly as may be, by means of the common tables, 
in the following manner. Since fin.p — fin. P fin. 
A-f-p, we have fin. p — fin. P fin. A cof. p 4- fin. P cof. 
A x fin. p, or fin. p ( 1 — fin. P cof. A) — fin. P fin. A 
cof. p; hence tang, p 
fin. P fin. A 
This formula 
1 — fin. P col. A* 
feems a little difficult to be wrought in numbers, but 
it is as eafyas the above one.; for, fuppofing fin. B*= 
fin. 
