264 COSMOS. 



to the simple supposition that the change ol velocity only 

 takes place in consequence of the action of a force, and that 

 forces act in obedience to the Newtonian laws." 



A year after Bessel's death, Fuss, at Struve's suggestion, 

 renewed the investigation of the anomalies of Procyon and 

 Sirius, partly with new observations with Ertel's meridian- 

 telescope at Pulkowa, and partly with reductions of, and 

 comparisons with, earlier observations. The result, in the 

 opinion of Struve and Fuss" proved adverse to Bessel's 

 assertion. A laborious investigation which Peters has now 

 completed at Konigsberg, on the other hand, justifies it; as 

 does also a similar one advanced by Schubert, the calculator 

 for the North American Nautical Almanack. 



The belief in the existence of non-luminous stars was 

 diffused 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 

 vapours, there revolve certain other earthlike bodies, which, 

 however, remain invisible to us." 18 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 conjec- 

 tured 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 conviction 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 sur- 

 passed the brilliancy of Jupiter, have not changed their place 



11 Struve, Etudes d'Astr. stellaire, Texte, p. 47, Notes, pp, 

 26, and 51-57 ; Sir John Herschel, Outl, 859 and 860. 

 u Origen, in Gronov. Thesaur.* t, x. p. 271. 



