116 



Rutherfurd Photographic Measures of 



61- Cygni 



AB = <r = True distance at 1873.546 from the 



mean of all the measured distances. 

 jSfZV= Distance measured on plate of the 



date, I, corrected except for proper 



motion. 

 P01 Po' = The proper motions of 6i l and 61 2 



Cygni at the epoch 1873.546. 

 AM, BN= Arcs traveled over in the time 



T = t — 1873.546. 

 A<r ]=The change in o- due to the proper 



motion of only 61 1 from A to M. 

 A'<r = The change in (o- — A<r ) due to the 



proper motion of only 61* from B to N- 



PAB = 7r = True angle at 1873.546 from the 



mean of all the measured angles. 

 PMN= Position-angle measured on plate 



of the date, t, corrected except for 



proper motion. 

 Xo , Xo ' = The position-angles of the proper 



motion of 61 1 and 61 2 at 1873.546. 

 PBA = A ', also y, z, K are auxiliary angles 



having the significance shown above. 

 A7r =The change in 7r due to the proper 



motion of only 61 1 from A to M. 

 A'7r = The change in (n — An ) due to the 



proper motion of 61 2 from B to N. 



