Sixty-five Stars near 61 Cygni. 61 



the tangent correction only — which maj^ be obtained directly from 

 Table IY, being practically constant for each star — present all 

 the corrections which have been applied to the observed mean dis- 

 tance of the East and West impressions to get the corrected mean 

 of column eight. 



10. It is noticeable that among these corrected means the dis- 

 tances belonging to some of the plates are always larger than the 

 average and to other plates always smaller. To get rid of this 

 variation of scale value, whatever may be its cause, I have 

 selected the following four stars as standards : 



No. 



Distance. 



sin p. 



cos p. 



5 



77.2926 



— 0.998 



+0.054 



23 



89.2118 



—0.068 



+0.998 



32 



77.0019 



+0.127 



—0.992 



48 



50.7333 



+0.962 



— 0.274 



urns 



294.2396 



+0.02 



— 0.21 



Now, if s 5 , s 23 , s 32 , s 48 represent the distances of stars 5, 23, 32 

 and 48 from 6i l Cygni on any given plate and ^s s the sum of the 

 standard distances, there must be added to everjr distance on that 

 plate for any other star its proportional part of the difference be- 

 tween tbe mean of the sums of the distances of the standard stars 

 and their separate sums for that particular plate, or : 



Scale variation = lss ~ ^ + % + % 2 + %) g 



ZSs 



The following table gives the value of this coefficient of s for 

 each plate. The individual values of scale variation are given in 

 column nine of Table V. 



