some Stars towards or from the Earth. 141 



means of apparatus now being constructed, to be able to get more 

 accurate determinations of the velocity of the motions. 



Sirius. — The comparison of the line at F with the corresponding 

 line of hydrogen was made on several nights from January 18 to 

 March 5. Spectroscope C and eyepieces 2 and 3 were used. These 

 observations confirm the conclusion arrived at in my former paper, 

 that the star is moving from the earth ; but they ascribe to the star 

 a velocity smaller than that which I then obtained. 



These observations on different days show a change of refran- 

 gibility corresponding to a velocity of from 26 miles to 36 miles per 

 second. The part of the earth's orbital motion from the star varied 

 on these days from 10 miles to 14 miles per second. We may take, 

 therefore, 18 to 22 miles per second as due to the star. 



The difference of this estimate, which is probably below rather 

 than in excess of the true amount, from that which I formerly made 

 may be due in part or entirely to the less perfect instruments then at 

 my command. At the same time, if Sirius be moving in an elliptic 

 orbit, as suggested by Dr. Peters, that part of the star's proper 

 motion which is in the direction of the visual ray would constantly 

 vary*. 



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

 and myself on this star, we found that there are no strong lines coin- 

 cident 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 j3 

 occurs in the space between two groups of strong lines where the lines 

 are faint. On one night of unusual 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 co- 

 incident with H a, and a similar line at the position of H /3, These 

 lines are much less intense than the lines C and F in the solar spec- 

 trum ; 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 

 substances 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 dis- 

 tances 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 



* Dr. H. Vogel at Bothkamp seems to have repeated my observations on Sirius 

 with the necessary care. He says (Astron. Nachr. No. 1864) : — " Mit der eben 

 beschriebenen Anordnung gelang es Herrn Dr. Lohse und mir am 22. Marz 

 (1871) bei ganz vorzuglicher Luft die Nichtcoincidenz der drei Wasserstofflinien 

 H m, H (B, und H y, der Geissler'schen Eohre mit den entsprechenden Liniea 



des Siriusspectrum zu sehen mit Beriicksichtigung der Geschwindigkeit der 



Erde zur Zeit der Beobachtung bereehnet sich die Geschwindigkeit mit welehcr 

 sich Sirius von der Erde bewegt zu 1O0 Meilen in der Secunde, wogegeri Procyon 

 sich 13*8 Meilen in der Secunde von unserer Erde entlernen wurde." 



