PAR 



This formula was employed by Laeaille, at the Cape of Good Hope, 

 and Wargentin, at Stockholm, for finding the parallax of Mars. It can- 

 not be successfully applied to the Sun, or to Jupiter, Saturn, or tlu> 

 Georgian ; for where the parallax does not exceed 10 or 12 seconds, tl.e 

 probable errors of observation will bear so large a proportion to it, as 

 materially to affect the certainty of the result. 



The moon, however, whose parallaxes are considerable, is a proper 

 instance for the method, though in that case it will require some modi 

 fication ; as we must take into consideration the spheroidical figure of 

 the earth ; thus 



Let R be the radius of the equator, r and r' the radii of the earth at 

 the two places of observation, z and x 1 the zenith distances found as be- 

 fore, but corrected for the /'s between the vertical and the radius, then 

 the horizontal parallax at the equator is 



x + *' "" ( L L/ ) 

 r sin. z -J- r sin. K' 



3. The parallax of a planet in R. A. being found by observation, to find 

 its horizontal parallax. 



Let s be the R. A. in time, taken out of the meridian, then 



.p _^ 15 s x cos - ttec. 



cos. lat. x sin. hour angle 



If the R. A. be taken both before and after the meridian, and h and 7t' be 

 the two hour angles, and ,v the sum of the parallaxes in R. A. on the east 

 and west of the meridian, 



15 * X cos. dec. . 



P = 



cos. lat. x (sin. h -f- sin. /*') 

 15 .v x cos, dec. 



. h + h' h h r 



2 cos. lat. x sin. -~ x cos. - - 



4-. The greatest horizontal parallax of the sun and planets. 



Sun 8",75 Venus 29",1G Jupiter 2",08 



Mercury 14",58 Mars 17",50 Saturn. 1",027 



Georgian ... 0,"415, 



For Sun's parallax in altitude nee Sun, 



5. Parallax of the fixed stars. 



If t\\e anmial parallax does not exceed 1", the distances of the fixed 

 stars cannot be less than 206365 times the radius of the earth's erbit 16 

 1! M 



