174 



Astro7iomical and Nautical Collections. 



Note. If the declination is very small, it may sometimes be 

 more convenient to find the angle PAB from the three sides of 

 the triangle, as in the third precept, instead of the second. 



Example. 

 Let the two zenith distances corrected be ZA rz 73° 54' 13", 

 and ZB 47° 45' 51", the declinations 8° 18' and 8° 15', the 

 interval of time three hours, or PA = 81° 42', PB = 81° 45', 

 and APB zz 45°, whence | (PA + PB) = 81° 43' 30". The 

 operation will be thus : 



9.9954547 (i) 

 9.58-28397 (2) 



S — ZA= 9 11 0.5 



S— AB=38 34 50.5 



(ZB =47 45 51} 

 4 



2) 19.1695990 

 sin § BAZ=22° 36' 26".6 9.5847995 

 BAZ = 45 13 53 

 PAB = 86 33 58 

 PAZ=4l 26 5 



L. cos PA 

 cos ZA 



.040033 



9.1594354 

 9.4428780 



L. sin PA 

 sin ZA 

 cos PAZ 



9.9954271 

 1.9826314 

 9.8748934 



8.6023134 (15) 



712774 9.8529519 



.752797 N. sin 48° 50' 0", the Latitude required. 



00 



(12) 

 (13) 

 (14) 

 (16) 

 (17) 



ii. Computation of the Effect of terrestrial Refraction, in the 

 actual Condition of the Atmosphere. 



A. It is well known that a projectile, thrown in any oblique 

 direction, will acquire a height equal to the verse sine of twice 



