The Rev. Dr. Robinson on the Constant of Refraction. 223 



, , —2552.842 ^,^„o 



and du. = = — 0.1688 



^ 15118.944 



The correction for run for these stars give, 



and we have, 



fi = 57.7682 



— 0.1688 



— 0.0063 



57.5931 



which agrees so nearly with the determination from sub-polar stars (their dif- 

 ference being only 0".5 at Fomalhaut) that there is obviously no necessity for 

 supposing any discrepancy between the northern and southern refractions at 

 this observatory, especially as it would vanish entirely were the Cape declinations 



not used. If now we take u := 57.546 ; the value of — reduced to my latitude 



a 



is 0.00129263, and (using the well-known notation of Mr. Babbage to save 

 space) the equation of refraction becomes for t = 50, barometer 29-60, 



R = tang . e X log-' (1.7600151) 

 -f tang^ . e X log-' (7.9045751) {1 +tang^ . 6 X log. -' (6.44559)} 



— ^^ . 6 X log-' (8.8715498) {1 -f tang* . 6 X log. "' (6.77484)} 



+ ^^ . X log-' (6.3720995) {1 +tang* . 6 x log"' (7-06014)] 



— ^^ . 6 X log-' (4.0315728) {1 + tang* . 6 X log-' (7-23971)} 

 t»us 



+ ^^ . X log -' (1.7907405) {1 -f tang* . 6 X log"' (7-34007)] 



cos' 



