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



From this the following tables have been computed. In the first, the column 



X • .1 1 -1 pM(1 + 6(t— 50)) , , l-fe'(T — 50) 



A contams the logarithm of -^ — - ,-,, „^ -^, and b that of -—{ — 777 -— ;, 



29.0O \-\-e (T — 50) 



e' the expansion of the brass scale being taken = 0.0000 1 0479 ; and e" that of 

 mercury = 0.0001. 



The second table contains c, the sum of all the terms except the first, for the 

 argument zen. distance ; d =: the change of c for one degree increase gt tem- 

 perature ; and e its change for one inch rise of the barometer. This last serves 

 also to change c for a slight variation in /x, the constant, for 



fin 



-r = E X 0.5144 



and A must be changed by log /x' — log fi. 

 The refraction is given by 



log k' = A 4" B 4" log tang apparent zen. dist. -f- log. bar. 

 R = u' — c — D X (t — 50°) — EX (bar. — 29.60.) 



Argument of A, external thermometer = t 

 Argument of b, attached thermometer = t 

 Argument of c, d, and e, apparent zenith distance. 



