Solar and Planetary Evolution. 



69 



tent of the universe. Are there an infinite number of 

 worlds, extending beyond our utmost vision ? We cannot 

 know. All the objects within the reach of the most power- 

 ful telescopes belong to our universe. It is possible that 

 other universes exist beyond, which we are unable to per- 

 ceive because of the absence of a luminiferous ether, con- 

 necting them with our range of vision. It is an interest- 

 ing question whether our universe is still young and grow- 

 ing, or whether it is now on its downward course, tending 

 to decay and death. Respecting this question it may be 

 said that we find within the range of vision very few dead 



Fig. 13. Spiral nebula in Canes Venatici. 



stars, while the number of nebulae in process of forming 

 into stars is very great. We may therefore assume that 

 the universe is still in a youthful condition and has not 

 passed the noon of its existence. The spectroscope assures 

 us that those stars which shine with a red light are the old- 

 est, and the nearest extinction. Of these there are com- 

 paratively few. 



We have brought the history of a planet from the period 

 of its primal evolution out of the fiery mist, to its extinc- 

 tion. Is this all ? AVill there be no resurrection of dead 

 worlds ? When a planet like the moon has parted with its 

 heat it will still continue to rotate on its axis and to re- 



