306 Ruthei'furd Photographic Pleasures. 



The equations thus obtained are : 



Stars a, h -\- 1.9 146 iv + 0.4593 v — 0.2598 = o 



c, d + 1.8232 + 0.7773 — 0-1653 = o 



e,f — 0.8337 + 0.8176 — 0.3781 = o 



g,h —1.5436 + 1. 2615 —0.2318 = 0. 



*", j — 1.9961 -1-0.1171 -)-o.iii3^o 



Jc, I -f- 1.9950 — 0.0461 -|- 0.0698 = o 



from which the normal equations are : 



-j- 18,0319 w — 1. 4917 V — 0.2087 = o 

 + 5.7260 — 1. 2176 = o 

 and the solution gives : 



tv = -\- o.'"o298 ± o."oi47 



V = -\- 0.2204=1= 0.0264 



the probable error of one equation = ± o.'''o624 



Applying these corrections to the values previously' assumed, 



Corrected p sin y = + i.'"3i6o = Ja cos o 

 " rj cos y = — 0.4512 = Jo 

 which gives Ja = -|- o'.i6i7 Jo = — o.'"45i2 



corresponding to a motion of 1.^39 12 on a great circle whose 

 position angle is 108° 55' 30 ". 



Considering the difficulties that beset the investigation of the 

 parallax of this star, and the probability that all previous deter- 

 minations have been made with a single comparison star, which 

 may itself have a parallax ; considering also the large ditferences 

 exhibited by the- separate results of other observers, it would 

 seem that the result here given is not impossiblj^ large, if the 

 E.UTHERFURD plates are subject to no s^^stematic error. Whether 

 such error exist or not, these plates of rj Cassiopeite seem at any 

 rate entirelv unsuited for an investigation of it, and I have there- 

 fore in the preparation of this paper confined myself strictly to 

 the methods and formulae and oftea even to the phraseolog}' of 

 Professor Jacoby in his paper on u and Cassiopeiae, already 

 several times referred to, since this is but one in a series of many 

 papers to be pi'oduced from the Rutherfurd measures, and since 

 in siich a series uniformity is desirable. 



A catalogue of all the stars (62) on these plates has been re- 

 served for a separate paper which will be published soon, as No. 

 7 of Contributions from the Observatory of Columbia College. 



