50 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



while only six or seven of them have been previously used 

 in the similar investigations of Argelander,Madler, O. Struve, 

 Airy, Main, and others. In studying these stars. Professor 

 Safford states that he grouped them by tens, assuming those 

 to be equally distant whose proper motions in arc were near- 

 ly equal, and therefore leaving entirely out of consideration 

 the brightness of the stars. His first result, as regards the 

 direction of the movement of the solar system, was not very 

 different from those of his predecessors; but there appeared 

 indications that, for each of his groups of stars, the average 

 proper motion was inversely proportioned to the average 

 distance; in other words, that our assumption of stellar dis- 

 tances ought to depend upon proper motions. He concludes 

 that the stars having similar motions especially need study 

 at this time, and that eventually we may hope to use the 

 solar motion as a sort of base to advance our knowledsre of 

 stellar distances. This will be accomplished so soon as we 

 know the values of all the parallaxes that amount to or ex- 

 ceed one second ; and this may be soon determined by sys- 

 tematic co-operative arrangements among the astronomers 

 of the world. Proc. Am. Acad. Arts and Sci., 1875, 82. 



EXACT OBSERYATIOXS OF NEBULJi]. 



Dr. Schultz, of Upsala, has during the past ten years de- 

 voted a great deal of attention to the observation of nebulas, 

 having special reference to the determination of their precise 

 positions and motions. The results of his observations have 

 been jDublished as a catalogue of 500 nebulae, the whole num- 

 ber of single measures amounting to 12,000, a number which 

 is large enough to assure us of his great devotion to the 

 work. The heavens at Upsala are rarely free from clouds 

 for any length of time ; and the long twilights of summer, 

 the regular recurrence of bright moonlights, and the frequent 

 brilliant aurorse, have all combined to leave him but 404 

 working nights (or one night in ten in the course of eleven 

 years) that could be utilized for his delicate measurements. 

 The large number of aurora3 noticed by him will be an im- 

 portant minor result of his persistent labors. The telescope 

 employed by Dr. Schultz was of thirteen feet focal length, 

 whence we may gather that similar desirable work is fully 

 within reach of a number of telescopes in the United States. 



