EICHELBERGER : DISTANCES OF HEAVENLY BODIES 



171 



Within fifteen years after this statement by Pond, obser- 

 vations had been obtained which showed a measurable parallax 

 of three different stars. The announcements of these results, 

 each by a different astronomer, were practically simultaneous. 



W. Struve, using a filar micrometer, determined the distance 

 of a Lyrae from a small star about 40" distant on 60 different 

 days over a period of nearly three years. He obtained a parallax 

 of // .262 ± 0".025. Bessel, using his heliometer, determined 

 the distances of 61 Cygni from two small stars distant about 

 500" and 700" respectively. He obtained for this star a parallax 

 of 0".314 ± 0".020. Henderson, using determinations of the 

 position of a Centauri by meridian instruments, deduced a 

 parallax of 1".16 ± 0".ll. All three of these results were 

 announced in the winter of 1838-39, and indicate that the three 

 stars are distant from the Earth about 750,000, 650,000, and 

 200,000 times the distance of the Sun from the Earth. 



TABLE II 

 Parallax of 61 Cygni 



MEAN DATE 



1837 August 23.... 

 September 14 

 October 12. . . 

 November 22. 

 December 21. 



1838 January 14. . . 

 February 5. . . 



May 14 



June 19 



July* 13 



August 19 



September 19 



OBSERVED 

 DISPLACEMENT 



+0.20 

 +0.10 

 +0.04 

 -0.21 

 -0.32 

 -0.38 

 -0.22 

 +0.24 

 +0.36 

 +0.22 

 +0.15 

 +0.04 



COMPUTED FROM 

 0"314 



+ 0.18 

 + 0.08 



-0.05 

 -0.22 

 -0.27 

 -0.27 

 -0.23 

 +0.20 

 +0.28 

 +0.28 

 +0.19 

 +0.06 



Table II exhibits the observed displacement of 61 Cygni by 

 monthly means as given by Main from Bessel's observations. 

 The last column gives the computed displacement on the assump- 

 tion of a parallax of 0".314. The reality of the parallax is seen 

 at a glance. 



