190 ON THE ORIGIN OF THE PLANETARY SYSTEM. 



reverted to the darkness from which it had so suddenly 

 emerged. The largest of them all seems to have been 

 that observed by Kepler in the year 1604, which was 

 brighter than a star of the first magnitude, and was 

 observed from September 27, 1604, until March 1606. 

 The reason of its luminosity was probably the collision 

 with a smaller world. In a more recent case, in which 

 on May 12, 1866, a small star of the tenth magnitude 

 in the Corona suddenly burst out to one of the second 

 magnitude, spectrum analysis showed that it was an 

 outburst of ignited hydrogen which produced the light. 

 This was only luminous for twelve days. 



In other cases obscure heavenly bodies have dis- 

 covered themselves by their attraction on adjacent 

 bright stars, and the motions of the latter thereby pro- 

 duced. Such an influence is observed in Sirius and 

 Procyon. By means of a new refracting telescope 

 Messrs. Alvan Clarke and Pond, of Cambridge, U.S., 

 have discovered in the case of Sirius a scarcely visible 

 star, which has but little luminosity, but is almost 

 seven times as heavy as the sun, has about half the 

 mass of Sirius, and whose distance from Sirius is about 

 equal to that of Neptune from the sun. The satellite 

 of Procyon has not yet been seen; it appears to be 

 quite dark. 



Thus there are extinct suns. The fact that there 

 are such lends new weight to the reasons which per- 



