EICHELBEEGER : DISTANCES OF HEAVENLY BODIES 167 



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 

 almanacs twenty years ago, corresponds to a distance of 92,900,- 

 000 miles. At present it seems improbable that another paral- 

 lax campaign will be undertaken before 1931, when Eros ap- 

 proaches 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 



275 B.C. to 1620 A.D. 



1620 Kepler 



1672 Flamsteed 



1916 



When Copernicus proposed 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. However, the 

 system was generally accepted as the true one and the determi- 

 nation of stellar parallax or the distance of the stars became a live 

 subject. Picard in the latter half of the seventeenth century, 

 using a telescope and a micrometer in connection with his divided 

 circle, showed an annual variation in the declination of the pole 

 star amounting to 40". In 1674 Hooke announced a parallax of 

 15" for y 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. 



The period which we have now reached is so admirably treated 

 by Sir Frank W. Dyson, Astronomer Royal, in his Halley Lee- 



