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: 3 THE STARRY HEAVENS 471 
therefore invisible, companion. The spectro- 
scope, in fact, makes known to us the 
presence of many stars which no telescope 
could reveal. 
Thus the floor of heaven is not only 
“thick inlaid with patines of bright gold,” 
but studded also with extinct stars, once prob- 
ably as brilliant as our own Sun, but now 
dead and cold, as Helmholtz tells us that our 
Sun itself will be some seventeen millions of 
years hence. 
Such dark bodies cannot of course be seen, 
and their existence, though we cannot doubt 
it, is a matter of calculation. In one case, 
however, the conclusion has received a most 
interesting confirmation. The movements of 
Sirius led mathematicians to conclude that it 
had also a mighty and massive neighbour, the 
relative position of which they calculated, 
though no such body had ever been seen. In 
February 1862, however, the Messrs. Alvan 
Clark of Cambridgeport were completing 
their 18-inch glass for the Chicago Observa- 
tory. “Why, father,” exclaimed the younger 
Clark, “‘the star has a companion.’ The 
