The Rutherfurd Photographic Measures. 125 



from column eight, Table VI, be used, the equations of condi- 

 tion can be formed as in Table XVIII. The solution of these 

 equations is given at the bottom of each page ; where also will be 

 found the probable errors of the unknowns ; likewise the prob- 

 able error of one equation of unit weight expressed as change of 

 position-angle and also as reduced to the arc of a great circle by 

 aid of the 



"Factor" = 28 // .oi24 • a -sin i // = [6.1329] a 



36. The values of parallax given by the measures of distance 

 of the various pairs of stars are collected in the first part of Table 

 XV, with their weights, p, deduced from the least-square solu- 

 tion, and the corresponding probable errors, r„. As the stars 5 

 and 6 enter respectively into each of two pairs, the " combining 

 weights " of those pairs, (p), were used in computing the mean 

 of the five determinations. The (r^) is the probable error of the 

 parallax when (p) is regarded as the weight. Hence 



Parallax = -f- o // .3999 ± o // .0230. 



In the second part of Table XV are given the values of 

 parallax deduced from the measures of position-angle, with their 

 probable errors r„. Hence 



Parallax = + o // .3326 ± o // .oi89. 



When these two values are combined with weights which are 

 the reciprocals of the squares of their respective probable errors 

 there results the 



Mean relative parallax of 61 1 Cygni = + o // .36o ± o // .oi46 



