April 17, 1903.] 



SCIENCE. 



603 



Took part in all the deliberations of the 

 commission, devising most of the instru- 

 ments used by the observing parties, and 

 was actively engaged for more than two 

 years in fitting out the various United 

 States expeditions. Attained the relative 

 rank of commander May 31, 1872. Was 

 attached to the United States steamer 

 Swatara from June 3, 1874, to June 3, 

 1875, during her voyage to the southern 

 hemisphere with the United States transit 

 of Venus parties, and visited all the points 

 at which she touched. His own station 

 was at Hobart, Tasmania, and after suc- 

 cessfully observing the transit of Venus 

 there on December 9, 1874, he accompanied 

 the Sivatara to the German transit of 

 Venus station on Auckland Island, in lati- 

 tude 50° 56' S., and to the United States 

 station on Chatham Island, and finally left 

 her at Melbourne, returning to Washing- 

 ton via the Hawaiian Islands and San Fran- 

 cisco, thus making a complete tour around 

 the world. On June 22, 1875, was assigned 

 to special duty at the Naval Observatory 

 in connection with the reduction of the ob- 

 servations made by the United States trans- 

 it of Venus parties. The records obtained 

 by them consisted principally of wet col- 

 lodion photographs upon glass plates, show- 

 ing an image of the sun about four inches 

 in diameter, with Venus upon it, and the 

 problem before Professor Harkness was to 

 devise instruments and methods for meas- 

 uring these photographs which would give 

 the relative positions of Venus and the 

 sun with the utmost accuracy. This he 

 accomplished in an entirely satisfactory 

 manner, although the difficulty of the prob- 

 lem was so great that the most eminent as- 

 tronomers of England and Germany failed 

 to obtain any useful results from the photo- 

 graphs taken by their parties. While en- 

 gaged upon the transit of Venus reduc- 

 tions, in 1877, he invented the spherometer 



caliper, which is probably the most accurate 

 instrument known for determining the 

 figure of the pivots of astronomical instru- 

 ments, and in 1879 he discovered the theory 

 of the focal curve of achromatic telescopes, 

 which is now universally used for exactly 

 defining their color corrections. In April 

 and May, 1876, he set up the government 

 astronomical exhibit at the Centennial Ex- 

 position in Philadelphia, Pa. Attained 

 the relative rank of captain April 17, 1878. 

 Observed the transit of Mercury of May 6, 

 1878, at Austin, Texas, and the total solar 

 eclipse of July 29, 1878, at Creston, Wyom- 

 ing, having charge of the United States 

 Government parties at these places, and 

 subsequently edited the quarto volume of 

 430 pages containing the reports on the 

 eclipse, which was issued by the Naval Ob- 

 servatory in 1880. Immediately there- 

 after he took up the photographic observa- 

 tions of the transit of Mercury, and they 

 were reduced under his supervision in 1880 

 and 1881. At the same time he also car- 

 ried out some rather extensive experiments 

 in astronomical photography, including the 

 spectra of the sun and moon, with the view 

 of ascertaining the most suitable kind of 

 pyroxyline, and the best form of apparatus 

 for photographing the corona during total 

 solar eclipses. In 1881 to 1883 he was en- 

 gaged in reducing the zones of stars ob- 

 served by the late Captain James M. Gil- 

 liss, at Santiago, Chile, during the years 

 1849-52 ; but that work was suspended for 

 want of funds on June 30, 1883, and was 

 not completed and published until 1895. 

 On account of the failure of the English 

 and German astronomers to obtain any 

 satisfactory results from their photographs 

 of the transit of Venus of December, 1874, 

 they decided not to employ photography 

 in observing the transit of December, 1882, 

 and a very prominent American astron- 

 omer urged the United States Transit of 



