1845.] Astronomical refractions. 3 



Then as far as 80° of Zenith distance the log mean refraction is 

 equal to Log. P. From Table i. 



+ Log. T. From Table ii. 

 -f- Log. Z. From Table hi, 

 and to the refraction so found, must be applied the following correc- 

 tions when the Zenith distance exceeds 80° vizt. 

 _ T. (T. — 50°.) 

 — b. (30 in.— p.) 

 The values of T. and b. will be found in Table iv. 

 Example I. The observed Zenith distance of Capella being 

 80°, 24', 09."4. 



The height of the Barometer 29.73 and the Temperature 47-°75. 

 Fahrenheit required the refraction ? 



Log. P. 29.73 Table, i 9.99607 



Log. T. 4775 Table, 11 0.00214 



Log. Z. 88°: 20': 00 Table, in 3.08087 



Propl. partfor04':09".4 = 04'.157 840 



Nearest Tabular refraction, . . . . 20': 04".68 3.08748 



Log. diff. 661 -r- 36 or Tab. diff. for 1".= -f 1837 

 T. (T.— 50°) (Table iv.)= —.92 + — 2.°25= + 2 32 

 b. (30 in. p.) (Table iv.)= —167 +, + .27= — 0.45 



Mean refraction, 20' : 24".92 



Example II. From the appendix to the Greenwich Transactions 



for 1836. 



To find the refraction for Zenith distance 83°. 22', the Barometer 



reading being 29.63 and Thermometer 58°. 1. 



Log. P. 29.63 Table, 1. 9.99461 



Log- T. 58.°1 Table, 11. 9 99239 



Log. Z. 83° 20' Table, in 2.66759 



Propl. part for 02' , 190 



Nearest Tabular refraction, . . ...fi 30".21 2.65641 



