Sixty-five Stars near 61 Gygni. 



The significance of S 8 and S 9 will be found in paragraph 22, and 

 of S 7 in paragraph 17. 



20. It is easily seen that both A and B cannot be satisfied at 

 the same time, unless the direction of proper motion of the prin- 

 cipal star coincide with the major or the minor axis of the paral- 

 lactic ellipse. Tins fortunately is very nearly the case with 61 x 

 Gygni ; wherefore it would have been immaterial here whether the 

 angles of the standard stars had been corrected for proper motion 

 or not, though as a matter of fact they were so corrected ; as would 

 ordinarily be necessary. 



21. If stars can be found on all the plates which will satisfy 

 only very closely, but not exactly, condition A, the residuum of 

 the parallactic effect may be more nearly eliminated by adding to 

 the orientation variation deduced from such stars the quantity 



(A' 



P s )2° 2 S 1+ (P/-P i )2c% 



2o 2 



2(7 2 



n' 



where the primed P s f and P± are the means of the values of P z 

 and P 4 for all the plates, and where II' is an approximate value of 

 the parallax, or a value deduced from the measures of distance. 



In this paper the following six stars were selected as the 

 standards : 



Star 



5 

 6 



13 

 23 

 32 



—423898.2 

 — 90170.0 

 — 611921.1 

 —459811-3 

 +418587.4 

 +322758.0 



These give : 

 2W& 



+227748.4 

 +550938.7 

 —381846.5 

 — 441482.6 

 +364040.6 

 — 85914.0 



2ff2 



==— 20.5 



Zff*& 



S 7 

 +o.oc£ 



— .000240 

 + .009566 

 + .009229 



— .011118 



— .016022 



5962. 

 9017. 

 9667. 

 7969. 



59 2 9- 

 2580. 



2<7 2 



+ 5-7 2S 1 = — .000003 



which shows that the3 T are admirably adapted to the present pur- 

 pose. From these stars, therefore, and with W = +o/ / 40 have 

 been deduced the following corrections, additive to observed 

 position-angles. 



