268 



Rutherfurd Photographic Measures. 



which is additive to observed distances. If we substitute in the 

 above formulas the co-ordinates of the central star 24 p; viz : 



a = 54° 57' 3 = +23° 43' 



we get the following expressions for the correction to reduce the 

 observed values to 1873.0: — 

 For the position angles : 



J r l 7"-9 J r I - 2 53 6 ]-4+ [«9-7974]# + [719. 4020] C-\- [719.5560]!), for plates 



taken in 1872. 

 -f [w 1. 2536]^ + [>9.7974]£+ [719.4020] C-\- [«9.556o]Z>, for plates 



taken in 1873- 



— i7 // .9 4-[ni.2536]^.-f [«9-7974]^+ [7*9.4020] C-f [719.5560]/), for plates 



taken in 1874. 



For the distances : 



s {[4. 65 1 3] C -f- [^4-4064] Z)}, for all plates. 



If we apply these formulae to the several plates we find the fol- 

 lowing values of the position angle corrections, and of the factor 

 for correcting the distances : 



Plate. 



Position Angle 



Distance 





Correction. 



Factor x io 3 . 



16 



+ i8 / -5 



—.0769 



17 



4-18.5 



—.0769 



18 



4-20.0 



— .0918 



19 



—33-5 



-}-■ 0217 



20 



—33-5 



-J-.0217 



21 



—33-5 



-j— 0217 



22 



—33-9 



4-.OI30 



23 



—33-9 



+.OI30 



24 



—34-9 



— .OIII 



25 



—34-9 



— .OIII 



The values are the same for Eastern and Western impressions. 

 The distance corrections have been computed with Crelle's tables 

 by simply multiplying the factor given above by the number of 

 thousands in the distance s. The position angle corrections, being 

 constant for the whole plate, have been incorporated with the " zero 

 correction," as will be explained later (see VI.). 



