152 REPORTS ON INVESTIGATIONS AND PROJECTS. 



the practice of the three fundamental observers, Tucker, Roy, and Varnum, 

 to make some observations in the late afternoon, but the principal part of 

 them in the first half of the night. Observations were also made by them 

 for a short time in the morning in order to secure a group of fundamental 

 stars, approximately 12 hours later than observations of fundamental stars 

 the evening before, and at the same time to obtain transits of close-polar 

 stars, successively above and below pole, in order to determine the azimuth 

 of the instrument, independently of any knowledge of the right-ascension of 

 any polar stars. The office of the groups of fundamental stars, approx- 

 imately 12 hours apart, is to obtain corrections of the "clock-stars" free from 

 diurnal period. The fundamental observers also observed for determination 

 of the standard stars in all zenith-distances from about 8o° north to 8o° 

 south, and aimed to obtain, in one class 8 and in another class 12 observations 

 each. As they had opportunity, they also observed for determination of the 

 places of those stars that are brighter than the seventh magnitude, or that are 

 contained in La Caille's zone-catalogue for 1750. Each of these stars, not 

 included in the classes of standards, was scheduled to have four observations. 



Each of the three fundamental observers was assigned to primary observa- 

 tions for one week and was then followed by another, who assumed the 

 responsibility for all primary observations during the next week. Quite fre- 

 quently the fundamental observers not on duty with primary observations 

 were engaged during the last half of the night on secondary observations. 

 The observers Zimmer and Sanford were always engaged on secondary ob- 

 servations, and usually for the later hours of the night. 



While one observer was engaged at the telescope, another read the micro- 

 scopes, recording the indications of each of the four microscopes at each 

 setting. Following was the approximate number recorded by each of the 

 readers: Fair, 12,000; Delavan, 16,000; M. I. Roy, 3,500; Mearns, 14,500; 

 Jenkins, 16,500; Sanford, 6,300; Zimmer, 4,800; fundamental and miscella- 

 neous, 4,400. 



Almost invariably the chronograph sheets were read off on the day follow- 

 ing observations, so that the observing list could be carefully checked off, and 

 observations superfluous to the program avoided. Computation of the wire- 

 intervals and of the inclination of zenith-distance wire were kept nearly up to 

 date. Nearly 2,600 sets for wire-intervals have been obtained in all, about 

 equally in the two clamps. In the first 334 series 725 determinations of 

 magnitude-equation were made by the five telescope observers — mainly by the 

 three fundamental observers. Up to July 4, 19 10, from 40 to 70 single deter- 

 minations of the difference of transit north minus south were made by each 

 observer, or 270 in all. This part of the work is still considerably in arrears. 



As soon as the first general determination of wire-intervals was obtained, 

 the staff in San Luis applied the results to the reduction of transits to mean 

 wire. 



The means of the microscopes and the application of the correction for 

 errors of runs were currently made. 



