1 882. 51 Trans. N. Y. Ac. Set. 



the President. Prof. J. K. Rees, Director of the Columbia College 

 Observatory, presented a report (published in the Annals) upon 



OBSERVATIONS OF THE TRANSIT OF VENUS. 



(Abstract). 



The station occupied was the roof of the unfinished observatory of 

 the college. The telescope was placed in the southwest corner of the 

 roof. This roof is extraordinarily strong and solid, the beams being of 

 iron, twelve inches in depth. Solid brick arches spring from beam to 

 beam. The height of the roof from the street is about one hundred 

 and ten feet. The walls supporting the roof are four feet thick. An 

 unobstructed view was had of the whole transit. The position of the 

 instrument was only a few feet from the old observatory, so that we 

 may take the longitude and latitude of our instrument from the Ameri- 

 can ephemeris : — 



Latitude, + 40° 45' 23" .1. 



Longitude :— From Washington, — oh. 12m. 18.40s. 



Longitude: — From Greenwich, + 4h, 55m. 53.69?. 



"The timepieces used were a mean time chronometer, No. 1853, 

 made by Parkinson & Frodsham, of London, England, and a sidereal 

 chronometer, No. 1564, made by Negus & Co., of New York City. The 

 instrument used in the observations was an equatorially mounted refrac- 

 tor by Alvan Clark & Sons. Aperture, 5.09 inches ; focal length of 

 object glass, 74.3 inches. The magnitymg powers used were 48 on the 

 I. contact, 165 on the It. and III. contacts, 95 on the IV. contact. 

 The telescope was moved by clockwork, supplied with a Bond spring 

 governor. In making chronometer comparisons, the sidereal chronome- 

 ter was left at the college, and the mean time chronometer was carried 

 to the instruments on which signals v/ere to be received. 



Professor Rees had prepared, but omitted to give, an elaborate 

 system of chronometer comparisons with the Western Union time sig- 

 nals and the Washington time signals. The object of the comparisons 

 was to obtain the exact error of the chronometer used at the time of 

 the observations. 



Adopted Contact Times, 



Mean Time Mean Time 

 of Columbia in Wash- 

 College, ington. 

 H. M. S. H. M. S. 



I ■*2I 8 50.0 20 56 31.6 



II 21 28 43.9 21 16 27.5 



in 2 52 13.5 2 39 55.1 



IV t3 II 52-1 2 59 33.7 



* Notch plainly on. Estimated a minute late. 

 + Poor contact. Cloudy. 



