The Milky Way 



11 Star, send me a single one of thy rays and I 

 will tell thee what thou art! " However, our 

 enumeration is incomplete; in the midst of the 

 innumerable incandescent stars a single cold 

 one, Algol's companion, has been discovered by 

 chance. But the universe is full of these dead 

 stars, though we are blind to their existence, 

 and if all these orbs could suddenly blaze forth 

 great would be the increased beauty of the 

 heavens! We cannot rely on the method 

 which revealed Algol's companion for the 

 discovery in space of these obscure orbs. It 

 is only occasionally that one of these orbs 

 interposes itself between our eye and a bright 

 star. But science has other resources. If we 

 remember how Leverrier discovered the ex- 

 istence in the solar system of the hitherto 

 unsuspected planet Neptune, revealed by per- 

 turbations observed in the other planets, we 

 shall understand the principle which enabled 

 Bessel to conquer this invisible world. A star, 

 without any near neighbours in the heavens, 

 should move in a straight line, or rather describe 

 an almost circular trajectory round Madler's 

 central sun; but if it has invisible companions 



253 



