32 JOURNAL OF THE 



LATITUDE OF CHAPEL HILL. 



J. W. GORE. 



Prof. Julius E. Hilgard, chief of the United States Coast and 

 Geodetic Survey, kindly loaned the University a portable Transit, 

 Zenith Telescope and a Chronometer for the purpose of deteriuining 

 accurately the latitude of this place. 



Not knowing sidereal time, the transit had to be placed approxi- 

 mately in position by observations on Polaris. After leveling the 

 rotation axis and watching for Alioth or Epsilon Ursae Majoris and 

 Polaris to come into the same vertical circle, then following Polaris 

 for 17 minutes, fixing the instrument, which now is approximately 

 in the meridian. By observing some well known star, such as delta 

 bootis, which culminates near our zenith, we get a near approxima- 

 tion of sidereal time, and the chronometer was set. 



Then followed a series of oDservations on time stars for the pur- 

 pose of accurately adjusting the instrument in the meridian, and 

 also for determining the error of the chronometer and its rate. The 

 Zenith Telescope was easily set in the meridian by the aid of the 

 Transit, when the preliminary work was done and we were ready to 

 begin recording observations for latitude. 



Talcott's method by circumzenitli stars was followed. Several 

 pairs of stars are selected, such that the two of each pair do not 

 differ in zenith distance by more than about 20' of arc; one culmi- 

 ting north of the zenith and the other south. The difference in the 

 time of crossing the meridian must be sufficient to read the instru- 

 ment and turn it 180^ in azinuth, though not too long for fear of 

 changes in the state of the instrument. 



The Telescope is set at a zenith distance, which is the mean of the 

 zenith distances of the two stars, the star that culminates first is 

 observed and its position in the field of view is determined by the 

 micrometer, after noting the level the telescope is rotated 180^, about 

 its vertical axis, and the second star will be in the field of view as it 

 crosses the meridian, without altering the zenith distance of the 

 instrument; its position is also determined by the micrometer. Thus 

 the difference in the zenith distances of the two stars is determined, 

 which is the only quantity to be measured. 



Eight pairs of stars were observed, and twenty-five satisfactory 

 observations of pairs taken between June 15th and July 3rd. The 



