NEW MEASUEEMENTS OF DISTANCE OF SUN. 



109 



I suppose that there will always be two opinions upon the question : 

 Is the adojited value of the solar parallax to depend upon direct 

 observation or are the indirect determinations througli the constant 

 of aberration, the parallactic inequality, and the mass of the earth to 

 be allowed a weight in some proportion to their numbers? I take it 

 that those of us who have determined the parallax by direct obser- 

 vations may not unnaturally look upon these indirect methods as 

 interesting confirmations of our result if they agree with it. while if 

 they ditfer there must be something wrong with them. But in the 

 absence of a direct determination of overwhelming weight there 

 must ahvays be a feeling of uneasiness when one sees three or more 

 results conspiring to deny the truth of one. And hoAvever that may 

 be, it is certainly true that about the year 1898 there was a very gen- 

 eral suspicion abroad that the value 8 -80 seconds was too large. 



At this moment there came a curious stroke of fortune. Doctor 

 Witt, of the Urania Sternwarte, Berlin, was engaged in a photo- 



FlG. 1.— Eros campaign 1900-01. Distributiuii cii UljSLTvatorios.- 



graphic search for a minor planet which liad long been lost. He 

 failed, but found instead a minor planet for which one would will- 

 ingly barter the remaining five hundred odd; a minor planet indeed, 

 but moving in a most remarkable orbit, lying for the most part 

 within that of Mars, very eccentric, considerably inclined to the 

 elliptic, and ai)pr()aching the earth on favorable occasions within 

 about 15,000,000 miles. It was immediately i-ecognized that here was 

 a new opportunity for determining the solar parallax and that the 

 determination must be made at once or left alone for thirty years, 

 for a comparativeh' favorable opposition was due in U)00 and no 

 more good ones till 1930 and 1937. At the meeting of the permanent 

 connnittee which directs the nuUving of the astrographic chart and 

 catalogue of the whole sky it was resolved to invite a great coopera- 

 tion of observatories to make a combined onslaught on the j)i'oblem. 

 The suggestion was readily taken up, with an alacrity, indeed, which 

 might almost have suggested that the observatoi'ies concerned had 

 nothing to do and were glad of a job, an imputation which is innnedi- 



