DISTANCES OF HEAVENLY BODIES EICHELBERGEE. 173 



the Royal Astronomical 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 3O5OOO miles 

 in the distance to the sun. 



From a discussion of all the micrometric observations he obtained 



8''.806rt0''.004 



The observations with the meridian instruments gave 



8".837±0".0185 



a determination relatively much weaker than either of the others. 

 A parallax of 8". 80, the value adopted for all the national alma- 

 nacs 20 years ago, corresponds to a distance of 92,900,000 miles. At 

 present it seems improbable that another parallax campaign will be 

 undertaken before 1931, when Eros approaches still nearer to the 

 earth, its least distance at that time being about 15,000,000 miles. 



Table I. — Approximate distance from earth to sun as accepted at various times. 



Date. 



275B.C.tol620A. D. 



1620 Kepler 



1672 Flamsteed 



1916 



Distance. 



Mnes. 



4,500,000 

 13,500,000 

 81,500,000 

 92.900,000 



"\¥hen Copernicus pro])osed that the sun is the center of the solar 

 system and that all the planets, including the earth, revolve around 

 the sun, it was at once seen that such a motion of the earth must 

 produce an annual parallax of the stars. Tycho Brahe rejected the 

 Copernican system because he could not find from his observations 

 any such parallax. How^ever, the system was generally accepted as 

 the true one, and the determination of stellar parallax or the dis- 

 tance of the stars became a live subject. Picard in the latter half of 

 the seventeenth century, using a telescope and a micrometer in con- 

 nection with his di\dded circle, showed an annual variation in the 

 declination of the pole star amounting to 40". In 1674 Hooke 

 announced a parallax of 15" for 7 Draconis. About this same time 

 Flamsteed announced a parallax of 20" for a Ursae Minoris, but 

 J. Cassini showed that the variations in the declination did not 

 follow the law of the parallax. 



