DISTANCES OF HEAVENLY BODIES— EICHELBERGER. 

 Table II. — Parallaoa of 61 Cygni. 



177 



Mean date. 



Observed 

 displace- 

 ment. 



Computed 

 from 

 0".314. 



1837. 



August 23 



September It 



October 12 



November 22 



December 21 



1838- 



January 14 



February 5 



May 14 



June 19 



July 13 



August 19 



September 19 



+0.20 

 +0.10 

 +0.04 

 -0.21 

 -0.32 



-0.38 

 -0.22 

 +0.24 

 +0.36 

 +0.22 

 +0.15 

 +0.04 



+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 assumption 



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



glance. 



In 1888, 60 years after the first determination of what we now 

 know to be a true stellar parallax, Young, in his General Astronomy, 

 gives, in a list of known stellar parallaxes, 28 stars and 55 separate 

 determinations. Within the next 10 years the number of stars whose 

 parallaxes had been determined about doubled, due principally to 

 the^work of Gill and Elkin. 



Probably the most extensive piece of stellar parallax work in 

 existence is tliat with the Yale heliometer. The results to date 

 were published in 1912, and contained the parallaxes of 245 stars, 

 the observations extending over a quarter of a century, the entire 

 work having been done by three men — Elkin, Chase, and Smith. 

 In selecting a list of stars for parallax work, an effort is made to 

 obtain stars which give promise of being nearer than the mass of 

 stars. At first the brighter stars were selected, and then those with 

 large proper motions. The Yale list of 245 stars contains all stars 

 in the northern heajt^ens whose annual proper motion is known to 

 be as much as 0".5. Of these 245 stars, 54 are given a negative 

 parallax. A negative parallax does not mean, as some one has 

 expressed it, that the star is " somewhere on the other side of 

 nowhere," but such a result may be attributed to the errors of 

 observation or to the fact that the comparison stars are nearer than 

 the one under investigation. It is safe to say, however, that some- 

 what more than half of the 245 stars have a measurable parallax. 



Another series of stellar parallax observations, comparable in 

 extent with the one just mentioned, is that of Flint, at the Washburn 

 Observatory. This series includes 203 stars and extended from 1893 

 to 1905. These observations were made with a meridian circle, but 



