390 



Dr. W. Huggins on the Motions of 



[June 13, 



on account of the unfavourable state of the weather at the time) appear to 

 show that the stars Procyon, Capella, and possibly Aldebaran, are moving 

 from the earth. 



The stars which follow have a motion of approach. 



Arcturus. — In the spectrum of this star the lines of hydrogen, of mag- 

 nesium, and of sodium are sufficiently distinct for comparison. I found 

 the comparison could be most satisfactorily made with magnesium. 



The bright lines of magnesium fall on the less refrangible side of the 

 corresponding dark lines in the star's spectrum, showing that the star is 

 approaching the earth. I estimated the shift at about ^ to'l of the interval 

 between Mg 2 and Mg 3 ; this amount of displacement would indicate a 

 velocity of approach of 50 miles per second. To this velocity must be 

 added the earth's orbital motion from the star of 5*25 miles per second, in- 

 creasing the star's motion to 55 miles per second. 



When I can get favourable weather, I hope to obtain independent esti- 

 mations from the lines of sodium and of hydrogen. 



a Lyrce. — In the spectrum of Vega the line corresponding to H (3 is 

 strong and broad. Comparisons were made on several nights, but on one 

 evening only was the air favourable. The observations are accordant in 

 showing that the narrow bright line from a Geissler's tube fails on the less 

 refrangible side of the middle of the line in the star, thus leaving more of 

 the line on the side towards the violet. The estimations give a motion 

 of approach between the earth and the star of from 40 to 50 miles per 

 second, to which must be added 3*9 miles for the earth's motion from 

 the star. 



a Cygni. — The hydrogen line at F in the spectrum of this star is narrower 

 than in the spectrum of Sirius and of a Lyrse, though probably rather 

 broader than the same line in the solar spectrum. I have at present ob- 

 servations made on two evenings only, on both of which the state of the air 

 was unfavourable for the comparison of this line with that of terrestrial 

 hydrogen. They give to the star a motion of approach of about 30 miles 

 per second, which would have to be increased by 9 miles, the velocity at the 

 time of the earth from the star. 



Pollux. — The lines of magnesium and those of sodium are very distinct 

 in the spectrum of this star. As the air was not very steady at the time 

 of my observations, I found it more satisfactory to use for comparison the 

 lines of magnesium, which are rather stronger than those of sodium. The 

 three lines of magnesium appeared to be less refrangible than the cor- 

 responding dark lines in the spectrum of the star by about one sixth of the 

 interval from Mg 2 to Mg 3 . This estimation would represent a velocity of 

 approach equal to about 32 miles per second. The earth's motion from 

 the star was 17 "5 miles, which increases the apparent velocity of approach 

 to 49 miles per second. On one evening only was the air favourable 

 enough for a numerical estimate, but the observations were entered in my 

 observatory-book as satisfactory. 



