PROPER MOTION OF THE STARS. 187 



A. laborious investigation which Peters has now completed 

 at Kbnigsberg, on the other hand, justifies it ; as does also a 

 similar one advanced by Schubert, the calculator for the 

 North American Nautical Almanac. 



The belief in the existence of non-luminous stars was dif- 

 fused even among the ancient Greeks, and especially in the 

 earliest ages of Christianity. It was assumed that among 

 the fiery stars which are nourished by the celestial vapors, 

 there revolve certain other earth-like bodies, which, however, 

 remain invisible to us."* The total extinction of new stars, 

 especially of those so carefully observed by Tycho Brahe and 

 Kepler in Cassiopeia and Ophiuchus, appears to corroborate 

 this opinion. Since it was at the time conjectured that the 

 first of these stars had already twice appeared, and that, too, 

 at intervals of nearly 300 years, the idea of annihilation 

 and total extinction naturally gained little or no credit. The 

 immortal author of the Mecanique Celeste bases his convic- 

 tion of the existence of non-luminous masses in the universe 

 on these same phenomena of 1572 and 1604 : " These stars, 

 that have become invisible after having surpassed the brill- 

 iancy of Jupiter, have not changed their place during the 

 time of their being visible." (The luminous process in them 

 has simply ceased.) " There exist, therefore, in celestial 

 space dark bodies of equal magnitudes, and probably in as 

 great numbers as the stars."! So also Madler, in his Un- 

 tersuchungen uber die Fixstern-Systeme, says :$ "A dark 

 body might be a central body ; it might, like our own sun, 

 be surrounded in its immediate neighborhood only by dark 

 bodies like our planets. The motions of Sirius and Procyon, 

 pointed out by Bessel, force us to the assumption that there 

 are cases where luminous bodies form the satellites of dark 

 masses. "§ It has been already remarked that the advocates 

 of the emanation theory consider these masses as both invis- 

 ible, and also as radiating light : invisible, since they are of 

 such huge dimensions that the rays of light emitted by them 

 (the molecules of light), being impeded by the force of at- 

 traction, are unable to pass beyond a certain limit. H If, as 



* Origen, in Gronov. Tliesaur., t. x., p. 271. 



t Laplace, Expos, du Syst. du Monde, 1824, p. 395. Lambert, in his 

 Kosmologische Brief e, shows remarkable tendency to adopt the hypoth* 

 esis of large dark bodies. 



t Madler, Untersuch. uber die Fixstern-Systeme, th. ii. (1848), 8. 3» 

 and his Astronomy, s. 416. § Vide note t, p. 186 



II Vide supra, p. 88, and note.; Laplace, in Zach's Allg. Geogr 

 Epkem., bd. iv., s. 1 ; Madler, Astr., s. 393. 



