6 SIMON NEWCOMB— CAMPBELL. CMM °Tvo£xvn: 



and difficulties, and after experiment and trial proposed the following modifications of or addi- 

 tions to the more or less conventional program : 



1. The observations should be made with a photographic telescope, of long focus, whose 

 collimation axis should lie in the intersection of a horizontal plane and the plane of the meridian. 



2. A plumb line, consisting of very fine wire, should be suspended in front of the photo- 

 graphic plate, and as nearly as possible in contact with it, to form upon the plate a truly vertical 

 line to serve all purposes of orientation. 



3. Means should be provided to determine accurately the distance and any changes of 

 distance between the object glass of the telescope and the photographic plate throughout the 

 observation period. 



Prof. Newcomb, as secretary and member of the commission, bore a prominent part in the 

 preparation of a series of three papers relating to the transit of Venus in 1874, as a guide and 

 help to the observers, writing the first, On the Application of Photography to the Observation 

 of the Transits of Venus, and the third, On the Corrections to Hansen's Tables of the Moon's 

 Motion, needed in determining the longitudes of isolated observing stations. 



Plans for observing the transits of Venus were made also by the astronomers of Great 

 Britain, France, Germany, Denmark, Russia and Italy. Cooperation amongst the parties 

 from the different countries promised to be generally helpful, and with that policy in mind 

 Newcomb accepted an invitation to attend a meeting of the German commission, in Hanover, 

 in 1873. He endeavored to make clear the views of the American commission that valuable 

 results could not be secured by the system of photographing which had been proposed, but the 

 response was that the preparations had been advanced too far to admit of starting on a new plan. 



The Congress appropriated a total of $175,000 in the years 1872, 1873, and 1874 to finance 

 the program of the American commission. Expeditions were dispatched to three northern 

 stations, in China, Japan, and Siberia, and to five southern stations. Unfavorable weather 

 prevailed at all of the stations; failure from clouds was not complete at any station, but the 

 "value of the observations at every station was impaired. The results for the sun's distance 

 obtained by the co mmi ssions from the various countries were disappointing even where the 

 skies were clear. Newcomb was convinced that a better value for the radius of the earth's 

 orbit could be obtained by determining as accurately as possible the velocity of light and the time 

 which light requires to travel from the sun to the earth. He questioned seriously whether our 

 Government would be justified in dispatching parties to observe the transit of Venus in 1882. 

 The astronomers of this country were consulted, but only two negative voices, those of New- 

 comb and Pickering, were heard. The commission secured an additional appropriation of 

 $S5,000, and proceeded with the plans for observing the second transit. Prof. Newcomb con- 

 ducted the expedition to the Cape of Good Hope, where the sky on the day of the transit was 

 perfect and the observations were made as planned. Clear skies prevailed at about half of the 

 stations — four southern and five northern — and none of the observing parties failed completely. 



It was a matter of sincere regret to Prof. Newcomb that the results of the American observa- 

 tions have remained substantially unpublished. A preliminary discussion of some of the obser- 

 vations of 1874 made under the direction of the commission and edited by Newcomb, appeared 

 in 1880; but concerning the 1882 transit, nothing seems to have been published except brief 

 statements in an annual report of the Naval Observatory. Prof. Newcomb, as secretary of 

 the commission, was charged with the duty of reducing the observations and of preparing them 

 for the press. Small appropriations for assistants in this work had been made by the Congress, 

 but in the assignments of the reappropriations there were several slips, apparently beyond 

 Prof. Newcomb's control. The computers were discharged for lack of funds a first time, a 

 second time, and eventually a third time. Shortly thereafter, apparently in 1882, all of the 

 transit of Venus papers and results were turned over to Prof. Harkness, who reported progress 

 during a dozen succeeding years. Prof. Newcomb has recorded the opinion that the work is 

 "in that condition known in household language as 'all done but finishing.' Whether it will 

 ever appear is a question for the future." It is probable that all the men who ever had any 

 responsibility for, or serious knowledge of, the subject have passed away. In one sense, the 



