^B ESSAYS ANE) OBSERVATIONS 



12. It would be eafy, from the foregoing 

 rules, to conftruft tables of the parallaxes for 

 any given latitude. Such tables would be 

 fufficiently exadl, if calculated for every 

 third degree of the fun's longitude, and e- 

 very quarter of an hour from noon to 6 

 hours, affuming loooo for radius, or the ho- 

 riz. par. ^ a 0. The equation to be fubtra- 

 Oed from the apparent femid. needs only 

 be calculated for every loth degree of longi- 

 tude, and every half hour from noon to 6 

 hours, taking the mean femid. 0. 



1 3-. If the given time from noon be more 

 than 6 hours, fubtrad it from 1 2 hours, and 

 the Ion. from 12 figns ; and, for the re- 

 maining time and longitude, feek the intire 

 parallax, and the equation for the femid. 0^ 

 changing itslign. 



14. Such tables, tho' conftruded for a 

 particular latitude, may eafily be made to 

 ferve for any other latitude. For the varia- 

 tions from the meridian parallaxes are always 

 proportional to the cofine of latitude. And 

 the meridian parallax^ whether of Ion. or 

 lat. is made up of the fum or difference of 

 two parts J the firft of which is proportional 

 to the fine, the fecond to the cofine of lat. 



Thefer 



