departme;nt of meridian astrometry. i6i 



treme cases by over 5 magnitudes and the mean of the magnitudes which, 

 on a given night, would serve as the arguments for taking out the correction, 

 for the equation would ordinarily approximate to the fifth or sixth magni- 

 tude, with variations from this of the individual arguments ordinarily of less 

 than 3 or 4 magnitudes. 



Similarly the relative effect upon the time of transit was determined near 

 the zenith, depending upon whether the observer registers a transit as for a 

 north or as for a south star. The quantities exhibited in the following sum- 

 mary show the amounts that are to be applied to a transit south of the zenith 

 to make it homogeneous for the respective observers with their transits of 

 stars north of the zenith. The quantities are small, but in nearly every 

 instance are material. 



Transits of stars north minus south. 

 Observer. N.-S. 



R. H. Tucker —.011 



A, J. Roy —.036 



W. B. Varnum — .046 



M. L. Zimmer — .029 



R. F. Sanford — .018 



The care exercised in determining this quantity for each observer should 

 go far to compensate for any disadvantage that might be thought to arise 

 from the non-adoption of a reversing-prism. 



For polar stars of very high declination it was necessary to employ the 

 eye-and-ear method for transits, and in determining the polar deviation it 

 has been decided to employ that method as standard in taking the transits. 

 For all the observers except one the systematic difference between transits 

 obtained by that method from those obtained by chronographic registry was 

 carefully determined, so that the results by the two methods could be rendered 

 homogeneous. 



As will be seen from my report for 1910 (p. 154), about 400 transits by 

 reflection have been secured as a check upon systematic peculiarities in the 

 instrumental results, both in right-ascension and zenith-distance. The com- 

 parison between direct and reflected observations has not yet been made. 



It will be seen that the meridian-circle observations at San Luis were 

 completed much sooner than our early predictions (or estimates of possible 

 progress) would have led any one to anticipate. This remarkable result, so 

 contrary to ordinary experience, implies at the height of the work a yearly 

 rate of about 60,000 complete observations. This rate is fully four times 

 that usually attained for observations of this class, even in series where the 

 work has been prosecuted with considerable vigor. There are several expla- 

 nations for this. 



In the first place, there was an extraordinary number of clear nights, about 

 280 annually, or practically three times as many as are usually experienced 

 at any given observatory on the Atlantic seaboard of the United States. 



II — YB 



