OF ARTS AND SCIENCES. 15 



II. 



OBSERVATIONS OF THE TRANSIT OF VENUS, DE- 

 CEMBER 5 AND 6, 1882, MADE AT THE HARVARD 

 COLLEGE OBSERVATORY. 



By Edward C. Pickering. 



Presented December 13th. 1882. 



The chances of cloudy weather at this Observatory early in Decem- 

 ber are large, and Cambridge was not selected by the United States 

 Commission on the Transit of Venus as a station for observations of 

 the phenomenon. It therefore seemed injudicious to make any exten- 

 sive preparations for the occasion. The available telescopes at the 

 Observatory, however, were employed in observing the contacts. 

 Photometric and spectroscopic observations were also obtained with the 

 East Equatorial, and measurements of the diameter of Venus were 

 made with the telescope of Mr. Chandler, mounted in the West 

 Dome, and also with the East Equatorial. 



The morning of the transit was so cloudy that there seemed little 

 prospect of observing the contacts ; but the sua gradually became vis- 

 ible, and the clouds were thin enough at the time of ingress to allow 

 observation of both the first and the second contacts. The first part 

 of the afternoon was nearly clear, and the third contact was well seen. 

 A few minutes later the sun entered a mass of thin clouds, but was 

 still sufficiently well seen for observation of the last contact. 



Arrangements had been made before the day of the transit with the 

 "Western Union Telegraph Company for the distribution of the time 

 signals of this Observatory among those who might desire to obtain 

 them on December 6. The clock at which these si"-nals oriorinate 

 was carefully compared with the standard sidereal clock of the Obser- 

 vatory at frequent intervals, and also with the signals furnished by the 

 United States Naval Observatory at Washington, which were received 

 here by telegraph. To determine the error of the sidereal clock, ob- 

 servations were made with the meridian circle by Professor W. A. 

 Rogers, the results of which are given below. Since the transit, in 

 order to remove any doubts with regard to the error of the sidereal 

 clock as determined by a large fixed instrument, Professor Rogers has 



