414 THE BEATJTIES OF NATURE chap. 



proximately measurable. The first star to 

 which this test was applied with success was 

 that known as 61 Cygni, which is thus shown 

 to be no less than 40 billions of miles away 

 from us — many thousand times as far as we 

 are from the Sun. The nearest of the Stars, 

 so far as we yet know, is a Centauri, the dis- 

 tance of which is about 25 billions of miles. 



The Pleiades are considered to be at a dis- 

 tance of nearly 1500 billions of miles. 



As regards the chemical composition of the 

 Stars, it is, moreover, obvious that the power- 

 ful engine of investigation afforded us by the 

 spectroscope is by no means confined to the 

 substances which form part of our system. 

 The incandescent body can thus be examined, 

 no matter how great its distance, so long only 

 as the light is strong enough. That this 

 method was theoretically applicable to the 

 light of the Stars is indeed obvious, but the 

 practical difficulties are very great. Sirius, 

 the brightest of all, is, in round numbers, a 

 hundred millions of millions of miles from us ; 

 and, though as bright as fifty of our suns, his 

 light Avhen it reaches us, after a journey of 



