270 Rutherfurd Photographic Measures. 



IV. The distances of the stars from 24 p must be large, but not 

 large enough to bring them at all near the edges of the plate. 



The following stars were selected in accordance with these con- 

 ditions : 



Heliometer Approximate 



Star. Distance. Mag. Pos. Angle. 



// o 



Anon. 20 1700.64 8.0 0.8 



39 2896.67 7.7 61.4 



34 2436.45 7.2 I26.I 



23 1578.34 8.0 176.5 



1 1600.38 8.2 258.8 



4 1618.07 8.1 298.6 



11830.55 



The distribution in position angle is such that 



2 (sinp) = — 0.10 , s (cos p) = -|-o.i8 



The effect of any error in the heliometric place of 24 p upon the 

 sum of the distances will therefore be quite inappreciable. Using 

 then the above value (1 1830". 55) as the true sum of the six dis- 

 tances, we find for the various plates the scale values contained in 

 the following table. The value obtained for plate 21 depends upon 

 five stars only, as Anon. 4 was lacking on that plate. 



Plate. Scale Value. 



16 E. 



28.0157 



16 w. 



28.0178 



17 E. 



28.0146 



17 W. 



28.0156 



18 E. 



28.0141 



18 W. 



28.0147 



19 E. 



28.0117 



19 W. 



28.0127 



20 E. 



28.0113 



20 w. 



28.0122 



21 E. 



28.0107 



21 w. 



28.0.137 



22 E. 



28.0142 



22 W. 



28.0153 



23 E. 



28.0126 



23 W. 



28.0137 



24 E. 



28.0059 



24 W. 



28.0081 



25 E. 



28.0063 



25 W. 



28.0070 



