62 LIGHT SCIENCE FOR LEISURE HOURS. 



opinion we may form as to the distribution of the stars 

 in space. 



Before proceeding to indicate the bearing of recent 

 observations on these theoretical conclusions, I would 

 invite some t degree of attention to the circumstance 

 that the view I am here advancing as to the bearing of 

 new facts on the old hypotheses, is not a new one 

 framed to account for the new facts in a way agreeing 

 with my own theories respecting the stars. More than 

 three years ago in Fraser's Magazine, and earlier still 

 in the proceedings of scientific societies, I indicated my 

 belief that the real facts are precisely such as have now 

 been demonstrated. 



Already when I so wrote, promise had been afforded 

 that the astronomer might come in time to know, 1 not 

 merely whether certain stars are approaching or reced- 

 ing, but at what rate (in miles per second) these 

 motions are taking place. I need not here enter into 

 an explanation of the method by which this was to be 

 accomplished, inasmuch as a full account of the prin- 

 ciple on which the method is based is given in the 

 paper called c News from Sirius,' in my Essays on Astro- 

 nomy. Suffice it to say, that it depends on the observed 

 displacement of some known dark line in the rainbow- 

 tinted streak forming the spectrum of a star, and that 

 when such a line is displaced towards the red end of the 

 spectrum it is known that the star is receding, while 



1 See the closing words of the last paragraph but three in the essay 

 mentioned. 



