172 EICHELBERGER : DISTANCES OF HEAVENLY BODIES 



In 1888, fifty 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 ten 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 that 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 heavens 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 star's are nearer than the one under investigation. 

 It is safe to say, however, that somewhat 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 not after the method of a century ago. 

 The observations were strictly differential, the general plan 

 being to select two faint comparison stars, one immediately 

 preceding and the other immediately following the parallax 

 star, and to determine the difference in right ascension, the ob- 

 servation of the three stars occupying about five minutes. Here 

 as in the case of the Yale heliometer work a large proportion 

 of the resulting parallaxes are negative ; somewhat more than half, 

 however, were found to have a measurable parallax. The 



