214 Permanence of the Rutherfiird Photographic Plates. 



gardecl as the elementary one from a repetition of which all the 

 final results were obtained. 



Date, Dec. 31, 1895. 



X 



EAST 



Means 

 WEST 



Means 



STAR. 



SCALE. 



Difference 



of 



Means. 



Microm. 



Screw 



Corr. and 



Run. 



Div. 



Microm. 



Screw 



Corr. and 



Run. 



9-517 



-516 



9-5165 



9.009 



.Oil 



9.0100 



+ 67 

 + 80 



34 

 34 



9.709 

 .710 



9-7095 



9.218 



.219 



9-2185 



+ 61 



+76 



0.1930 

 0.2085 



—6 



—4 



Mean of Differences = m 

 Measured by Davis. % tn 



Division Error Corr. 

 Star 



0.2008 



0.1004 



+.0020 



34.1022 



—5 

 — 2 



The above is a measure of the a7-co6rdinate, corresponding to 

 the direction of right ascension on the plate. It is one of the 

 measures for which the position circle had been reversed through 

 an angle of 180°, so that operations i and 6 have been inter- 

 changed. This is the reason why the first reading on the star 



was made with the microscope screw set near 9.500. This par- 

 ticular measure was selected as an example because the run of the 

 naicroscope was : 



i2=+o.oi95, 



so that we can use the specimen table of run and screw-ei'ror cor- 

 rections given on p. 205. From that table are taken the numbers 

 given here in the columns headed " Screw Corr." The rest of the 

 above example requires little explanation. The column headed 

 " Div." gives the number attached to the line of the scale upon 

 which a reading was made. The screw corrections were not ap- 

 plied directly to the observations, but were carried along on the 

 narrow column on the extreme right, expressed in units of the 

 fourth decimal place. This column contains the difference of the 



