DOUBLE STARS. 199 



not the place to discuss the probability or improbability* of 

 such an hypothesis. Praise is, however, due to the eminent- 

 ly active director of the Observatory at Dorpat for having, 

 by his diligent labors, determined the positions and proper 

 motions of more than 800 stars, and at the same time ex- 

 cited investigations which, if they do not lead to the satis- 

 factory solution of the great problem itself, are nevertheless 

 calculated to throw light on kindred questions of physical 

 astronomy. 



VI. 



MULTIPLE OR DOUBLE STARS. THEIR NUMBERS AND RECIPROCAL 

 DISTANCES. PERIOD OF REVOLUTION OF TWO SUNS ROUND A COM- 

 MON CENTER OF GRAVITY. 



WHEN, in contemplating the systems of the fixed stars, we 

 descend from hypothetical, higher, and more general consid- 

 erations to those of a special and restricted nature, we enter 

 a domain more clearly determined, and better calculated for 

 direct observation. Among the multiple stars, to which be- 

 long the binary or double stars, several self-luminous cosmic- 

 al bodies (suns) are connected by mutual attraction, which 

 necessarily gives rise to motions in closed curved lines. Be- 

 fore actual observation had established the fact of the revo- 

 lution of the double stars.t such movements in closed curves 

 were only known to exist in our own planetary solar system. 

 On this apparent analogy inferences were hastily drawn, 

 which for a long time gave rise to many errors. As the 

 term " double stars" was indiscriminately applied to every 



the earth. But, according to the Iliad, i., v. 592, Hephaestus fell down 

 to Lemnos in one day, "when but a little breath was still in him." 

 The length of the chain hanging down from Olympus to the earth, by 

 which all the gods were challenged to try and pull down Jupiter (Il- 

 iad, viii., v. 18), is not given. The image is not intended to convey an 

 idea of the height of heaven, but of Jupiter's strength and omnipo- 

 tence. 



* Compare the doubts of Peters, in Schum., Astr. Nachr., 1849, s. 

 661, and Sir John Herschel, in the Outl. of Astr., p. 589 : " In the pres- 

 ent defective state of our knowledge respecting the proper motion of 

 the smaller stars, we can not but regard all attempts of the kind as to 

 a certain extent premature, though by no means to be discouraged as 

 forerunners of something more decisive." 



t Compare Cosmos, vol. i., p. 146-149. (Struve, Ueber Dopplesternc 

 *ach Dorpater Micnmeter-Messungen von 1824 bis 1837, s. 11.) 



