A. MATHEMATICS AND ASTRONOMY. 49 



star of the sixtli magnitude -with distinct bands, departing 

 in this respect from the cliaracteristics of both the third and 

 the fourth types, in which case, however, a short examination 

 revealed to him that he was examining the j^lanet Uranus, 

 and not a fixed star. Twice in the course of his sweeps 

 among the stars has he thus, with his small instrument, spec- 

 troscopically discovered this planet. Astr. iVacA.,LXXXV., 

 250. 



THE RESISTING MEDIUM EXISTING IN SPACE. 



The aro'ument for the existence of a medium in the inter- 

 stellar spaces which is sufficiently dense to aftect the move- 

 ments of the planets, comets, etc., has for a long time been 

 based solely upon the supposed retardation of the movements 

 of Encke's comet. This body completes its orbit around the 

 sun in about three years, but has of late ahvays appeared so 

 exceedingly faint as to be invisible except in the most pow- 

 erful telescopes. The accurate computations of Von Asten 

 havin<r shown him that the movements of this body, as ob- 

 served during the last ten years, could be accurately account- 

 ed for by a careful computation of the disturbing attractions 

 of the planets, he was led to predict the positions in which 

 the comet should appear during the spring of 1875, in which 

 predictions no allowance was made for the resistance oftered 

 to its motion by Encke's hypothetical ethereal medium. The 

 first glimpse of the comet during that season was obtained 

 by the observers at Washington in charge of the great equa- 

 torial. According to these and other astronomers, the comet 

 passed in the heavens through a path so nearly accordant 

 with Von Asten's predictions as to show that to account 

 for its motion during the last two or three apparitions no 

 recourse to the notion of a resisting medium is necessary. 

 Further investigations on this comet are in progress. V C, 

 XL, 45. 



MOTION OF THE SOLAK SYSTEM IN SPACE. 



In a recent contribution to the study of the motion of the 

 solar system in space. Professor Saiford, of Chicago, states 

 that his investigation is based upon the movements of the 

 250 stars examined by Argelander, for nearly all of which 

 Ave have very accurate determinations of the proper motions, 



C 



