The Rutherfurd Photographic Measures. 145 



The Parallax of 61 2 Cygni. 



37. If the coefficients for parallax of 6i 2 Cygni be computed by 

 the formulse of paragraphs 14 and 22, we have : 



S 3 = —0.296 S s = +9777. 



£4 = 822 &, = II20. 



With these, and the values of P 3 and P 4 of paragraph 14, have 

 been obtained the quantities printed in the last column of Table 

 XIII. 



38. The measured distances duly corrected for proper motions 

 of both stars are given in the last-but-one column of Table XIII. 

 Table XIX contains the equations of condition of the form : 



x -f (*-i8 7 3.5 4 6)y + (S S P, + BA) n + a — <r ' = o 



from which are derived the values of the unknowns given on the 

 same page. 



39. In column nine of Table XIII are given in like manner the 

 corrected position-angles from which the equations of condition 

 of Table XX have been formed after the manner of paragraph 35. 

 They are of the form 



a/ + (<— 1873.546)0' + ff-sin 1"- (5f 8 P 3 + ^P 4 ) n + ff.sin i"- (tt — V) = o. 



The resulting values of the unknowns will be found on the same 

 page. 



40. In both these cases, however, we cannot assume the parallax 

 of the reference star to be nil. Its value has been shown to be 

 + oZ'360 i'^ois- The mean by weight of the values of parallax of 

 61 1 with respect to 61 2 obtained from distance and from angle is 

 + o".o72 ± r/ .028, wherefore the concluded value of the 



Parallax of 61 2 Cygni = 0". 288 ± ".031 

 referred indirectly to all the comparison stars given in Table XIV . 



