Astronomical and Nautical Collections, 



317 



Example II. 

 Taken from Mr. Lax's Tables, p. 279. 

 30*4 inches, 

 30°. 



Hor. 



Apparent dist. 30 52 15 

 Par. 58 36 



No. I. 66812 

 260 



Same as by Mr. Lax's method . 130 



Here 6" and 38" are the variations of the star's and moon's re- 

 fractions, and 5" the variation of the auxiliary angle ; and they are 

 to be subtracted, as the true refraction is greater than the mean. 



Demonstration. — The correction of the auxiliary angle has 

 only to be demonstrated. In the investigation the parallax is 

 thrown out of consideration, as it is refraction alone which produces 



the effect. 



Let a = the auxiliary angle, 



M = moon's apparent altitude, 



S = sun or star's apparent altitude, 



r == moon's mean refraction, 



r = sun or star's mean refraction, 



mr m moon's true refraction. 



Then mr' = sun or star's true refraction. 



By the construction of Table IX., 2 cos. (60° + a) = 



cos. (M — mr) cos. (S — mr') 



cos. M cos. £ 



Vol. XX. Z 



