388 



Dr. W. Huggins on the Motions of [June 13, 



Betelgeux (a Ononis). — In the early observations of Dr. Miller and 

 myself on this star, we found that there are no strong lines coincident with 

 the hydrogen lines at C and F. The line H a falls on the less refrangible 

 side of a small group of strong lines, and H ft occurs in the space between 

 two groups of strong lines where the lines are faint. On one night of un- 

 usual steadiness of the air, when the finer lines in the star's spectrum were 

 seen with more than ordinary distinctness, I was able with the more 

 powerful instruments now at my command to see a narrow defined line in 

 the red apparently coincident with H a, and a similar line at the position of 

 H ft. These lines are much less intense than the lines C and F in the solar 

 spectrum ; there are certainly no bright lines in the star's spectrum at these 

 places. 



The most suitable lines in this star for comparison with terrestrial sub- 

 stances for ascertaining the star's motion are the lines of sodium and of 

 magnesium. The double character of the one line agreeing exactly with 

 that of sodium, and the further circumstance that the more refrangible of 

 the lines is the stronger one, as is the case in spectrum of sodium and in the 

 solar spectrum, and the relative distances from each other and comparative 

 brightness of the three lines, which correspond precisely to the triple group 

 of magnesium, can allow of no doubt that these lines in the star are really 

 produced by the vapours of these substances existing there, and that we may 

 therefore safely take any small displacement of either set of lines to show a 

 motion of the star towards or from the earth. The lines due to sodium are 

 perhaps more intense, but are as narrow and defined as the lines D x , D 2 

 in the solar spectrum : they fall, however, within a group of very fine lines ; 

 this circumstance may possibly account for the nebulous character which has 

 been assigned to them by some observers. 



The bright lines of sodium were compared with spectroscope B and eye- 

 piece 3 ; they appeared to fall very slightly above the pair in the star, 

 showing that the stellar lines had been degraded by the star's motion from 

 the earth. The amount of displacement was estimated at about one fifth 

 of the distance of D 1 from D 2 , which is probably rather smaller than the 

 true amount. This estimation would give a velocity of separation of 37 

 miles per second. At the time of observation the earth was moving from 

 the star at about 15 miles per second, leaving 29 miles to be due to the 

 star. 



When magnesium was compared, a shift in the same direction, and corre- 

 sponding in extent to about the same velocity of recession, was observed ; but, 

 in consequence of other lines in the star at this place, the former estimation 

 based on the displacement of the lines of sodium, was considered to be 

 more satisfactory. 



Rigel. — The lines of hydrogen are strong in the spectrum of this star, 

 and are suitable for comparison. 



The line II ft is not so broad as it appears in the spectrum of Sirius, 

 but is stronger than F in the solar spectrum : this line was compared by 



