172 



USE OF THE TABLES. 



Log A in minutes of a degree = Tah. I. + ar. comp. Tab. II. + Tab. III. 

 Log Bin minutes = Tab. I. + log :zTJFi + Tab. II. — log. 57,72 + log. barom. 

 — Tab. I. + Tab. II. + log. barom. + 7.2773. 



Log refraction in seconds = Tab. I. + log barom. + log tan (zen. dist A + B) 



If Table II. p. 103. vol. 12. Trans. R. I. Academy be added to 

 these they will serve for computing the refraction from the zenith 

 to the horizon. 



Example. 



App. zenith dist. (of « Lyrae S. P.) = 87<'.42'.10" Bar. = 29,50 & Therm. SS-jO* 

 Tab. I. for 870.42/17 gives 1.8160 



(ZD— A + B) 86.46,04 tan 11.2481 



Tab. II. 0.3039 



log Bar. 1.4698 



refr. 1051",5 log 3.0218 



= 17'3l",5 



The mean of 42 observations of n Lyrae S. P. made at the obser- 

 vatory of Trinity College Dublin, (mean of bar. 29,50 and mean of 

 therm. 35'')gave 17'.26',5. 



• Trans. R. I. Acad. vol. 12. p. 112, 



