X THE STARRY HEAVENS 417 



rate, and observation shows that the lines 

 given by the light of the two edges differ 

 accordingly. So again as regards the Stars, 

 we obtain a similar test derived from the 

 Earth's movement. As we revolve in our 

 orbit we approach or recede any given star, 

 and our rate of motion being known we 

 thus obtain a second test. The results thus 

 examined have stood their ground satisfac- 

 torily, and in Huggins' opinion may be relied 

 on within about an English mUe a second. 

 The effect of this movement is, moreover, 

 independent of the distance. A lateral mo- 

 tion, say of 20 miles a second, which in a 

 nearer object would appear to be a stupendous 

 velocity, becomes in the Stars quite imper- 

 ceptible. A motion of the same rapidity, on 

 the other hand, towards or away from us, dis- 

 places the dark lines equally, whatever the 

 distance of the object may be. We may then 

 affirm that Sirius, for instance, is receding 

 from us at the rate of about 20 miles a second. 

 Betelgeux, Rigel, Castor, Regulus, and others 

 are also moving away ; while some — Vega, 

 Arcturus, and Pollux, for example — are 

 2e 



