Sixty-five Stars near 61 Cygni. 



67 



effect of meridian-convergence upon the value of^at different dates, 

 we have for 6 1 1 Cygni: 



K= — 17'.2094 P 1 



the term in P 2 being neglected, as its maximum value in the 

 present research is only zbo/'ooois- 



The following table gives K for the various plates, and also the 

 values of P 5 ; while in columns four, five and six of Table YII 

 will be found S 5 , S 6 and S 7 . 





For Proper Motion. 



Plate. 









K 



P 6 



I 



+ 3-6 



— 43644- 



2 



+ 3-6 



— 43338. 



3 



+ 3-6 



— 43338. 



4 



+ 0.3 



— 3248. 



5 



+ 0.1 



— 1567- 



6 



+ 0.1 



— 1567- 



7 



+ 0.1 



— 1376. 



8 



— 2.8 



+ 33478. 



9 



— 2.8 



+ 33478. 



IO 



— 2.8 



+ 34oi3- 



ii 



— 2.8 



+ 34204. 



12 



— 2.8 



+ 34204. 



13 



— 2.8 



+ 34204. 



15 



— 4-5 



+ 54i9i- 



16 



-4.6 



+ 55338. 



17 



-4.6 



+ 55338- 



18 



-4.6 



+ 55452- 



19 



-4-6 



+ 55452- 



20 



-4.6 



+ 55452. 



19. Orientation Variation. — When the angles have been cor- 

 rected as described above, observation of the corrected mean plus 

 proper motion in Table YI reveals a variation of measures on 

 some of the plates from the mean of all that is erratic, and in 

 some cases very considerable in magnitude. This is undoubtedly 

 due to the method which Rutherfurd used for the orientation of 

 his plates. 



It was his custom in making the exposures to take two impres- 

 sions of the stars on each plate. After the second, or western 

 impression, the telescope clock was stopped, and the stars were 

 allowed to trail across the plate for a distance of sixty to eighty 



