DEPARTMENT 0? MERIDIAN ASTROMETRY. 

 Division-Correction. 



169 



In the annual report of this Department for 1909 some of these values 

 were, by inadvertence, miscopied. 



The close agreement of these determinations of errors of graduation, to- 

 gether with the agreement of the circle flexure, is sufficient proof that the 

 circles were unharmed in transportation to and from San Luis. 



The eccentricity has been determined for the San Luis reductions and 

 again when the instrument was set up at Albany, and the resulting correc- 

 tions applied to the individual graduations in tabular form. 



The corrections to be applied to north zenith-distances because of the 

 effect depending upon whether the observer faces north or south have been 

 determined and applied for the San Luis reductions. 



Corrections to zenith-distance observed feet north. 



PHOTOMETRIC OBSERVATIONS AT SAN LUIS. 



As has already been stated, the object of the photometric expedition to 

 San Luis has been the determination of the magnitudes of all those stars on 

 our meridian-circle program not determined elsewhere. For this work a 

 wedge-photometer has been used. In spite of the criticisms of this form of 

 photometer, the preliminary reductions would seem to indicate a degree of 

 accuracy comparable with that obtained from other forms of photometers. 



The photometric observing list has been finished from 4 h right ascension 

 to i6 h I5 m , according to the report received from San Luis (August 6, 1912). 

 From o h to 4 h the list is almost finished and from i6 h I5 m to i8 h 50 m it is 

 about half finished. About 13,500 observations have been taken of stars of 

 undetermined magnitude, and about 1,500 more observations have been taken 

 on fundamental stars for scale value, etc. 



The weather conditions at San Luis during the last year have been trying, 

 an almost unprecedented amount of cloudiness being recorded — quite a dif- 



