166 EICHELBERGER : DISTANCES OF HEAVENLY BODIES 



parallax campaign. Fifty-eight observatories took part in the 

 various observations called for by the general plan. The merid- 

 ian instruments determined the absolute position of Eros from 

 night to night as it crossed the meridians of the various observa- 

 tories; the large visual refractors measured the distance of 

 Eros from the faint stars near it, at times continuing the meas- 

 ures throughout the entire night; and the photographic equa- 

 torials obtained permanent records of the position of Eros 

 among the surrounding stars. In addition long series of obser- 

 vations had to be made to determine the positions of the stars 

 to which Eros was referred. 



When several years had elapsed after the completion of the 

 observations, and no general discussion of all the material had 

 been provided for, Prof. Arthur R. Hinks of Cambridge, Eng- 

 land volunteered for the work. The undertaking was truly 

 monumental. He first formed a catalogue of the 671 stars 

 which had been selected by the Paris Congress for observation 

 as marking out the path of Eros from a discussion of the results 

 obtained by the meridian instruments and from the photographic 

 plates. This done, with these results as a basis, a larger catalogue 

 of about 6000 stars had to be formed from measures on the 

 photographic plates. He was then ready to commence the 

 discussion of the observations of Eros itself. From 1901 to 

 1910 there appeared in the Monthly Notices of the Royal Astro- 

 nomical Society eight articles covering 135 pages giving the results 

 of his labors. 



From a discussion of all the photographic observations he 

 obtained a solar parallax of 



8".807 ± 0".0027 



a probable error equivalent to an uncertainty of about 30,000 

 miles in the distance to the Sun. 



From a discussion of all the micrometric observations he 

 obtained 



8".806 * // .004 



The observations with the meridian instruments gave 



