OF THE COSMOS. PROBLEMATICAL DARK STARS. 183 



or very near the sun. But since nothing in the motions 

 of our planetary system betrays the presence of an attract- 

 ing body of considerable mass at a very small distance, from 

 the sun, we are conducted back to the supposition of the 

 existence of such a body at a very small distance from a star. 



/ t/ / 



as the only valid explanation of an alteration in the propel 

 motion of the latter becoming visible in the course of 

 century." ( 299 ) In a letter to myself, in July 1844, (I had 

 sportively expressed some uneasiness at the idea of such a 

 ghost-world of dark stars), he said, "I do, indeed, con- 

 tinue in the belief, that Procyon and Sirius are both true 

 double stars, each consisting of one visible and one invisible 

 star. There is no a priori reason for regarding luminosity 

 as an essential property of bodies. The countless host of 

 visible stars clearly proves nothing against the possible 

 existence of an equally countless host of invisible stars. 

 The physical difficulty of a variation in the proper motion, 

 is satisfactorily met by the hypothesis of dark stars. The 

 simple supposition cannot be blamed, that an alteration of 

 velocity only takes place in obedience to a force, and that 

 forces act according to the Newtonian laws." 



A year after BesseFs death, Fuss, at Struve's instance, 

 renewed the investigation of the anomalies of Procyoii and 

 Sirius, partly by new observations with ErteFs Meridian 

 Telescope at Pulkova, arid partly by reductions and com- 

 parison with earlier observations. Struve and Fuss ( 30 ) 

 consider the result to be against BesseFs opinion. On the 

 other hand, a laborious inquiry, just completed by Peters 

 at Konigsberg, and a similar one by Schubert, the calcu- 

 lator employed on the North American Nautical Almanac, 

 support Bessel. 



