282 



Prsesepe Group; Measurement and Reduction 



Offset, 



0.0193 millimetres 



Eotation Corr'n., +0.0005 





— 0.0188 



In arc, 



— o // .99 



Transf. Corr'n., 



+ 1 -75 



Eefraction 



+ .24 



Corrected offset 



+ i".oo 



Position Angle, 



2 



270 + nr',9 



— (Aa> + £/?' + Cy' + DS'), + 2 .6 



20.06" sec <J sin a -t, -f- 84 .0 



True Position Angle, 270 + 198". 5 



Consequently we have from this star, 



r = + 0.000963 



Similar calculations for all the trails gave the following results 

 in which r has been multiplied 03- io 6 throughout. 



Orientation by Trails. Values of rX io 6 . 



^^-^^ Star. 















15. 



22. 



23. 



27. 



31. 



37. 



PlateT~^^ 















I 



+954 





+ 963 





+840 



+873 



III 



+334 





+39° 



+ Il8 



+288 





IV 



+851 





+777 





+757 



+706 



VII 



—128 



+186 



— 140 





— 52 





VIII 



+122 



+152 



+111 





+113 





IX 



—360 





—341 





—248 



—254 



Taking the mean for the four stars on each plate and setting 

 down again the values of r previously obtained by comparison 

 with the meridian observations, we have, 



Orientation by Orientation by 







Trails. 



Meria. Obs. 



Plate I 



+ 



3.000908 



+ 0.001054 



III 



+ 



282 



+ 409 



IV 



+ 



773 



+ 1435 



VII 



— 



34 



— 35 



VIII 



+ 



124 



+ 211 



IX 



— 



301 



— 326 



Means 



+ 



292 + 



458 



In comparing these it will be remembered that a difference of 

 0.000100 corresponds to about o".20 in the coordinates of the out- 

 lying stars of the group. The results are decidedly adverse to 



