STELLAR EVOLUTION. 313 



"We must look to the solar system for examples of stars in the last 

 stage of development. Each of the planets may in fact be regarded as 

 an object of this kind. The bare and rocky surface of the moon affords 

 a desolate picture of what may result from this long continued process 

 of condensation. The volcanic region which is shown to excellent 

 advantage in a photograph recently taken with the Yerkes telescope, 

 (Fig. 13) gives no evidence of the existence of life; in fact, the spectro- 

 scope indicates that if there is any air on the moon it is much too rare 

 to support life as we know it. 



Fortunately, the moon is not the only example of a worn-out 

 star. The earth, which probably has many counterparts in the universe, 

 is another example of a less desolate kind. Here, though the process of 

 condensation which is the chief cause of celestial phenomena has ceased, 

 the problem of evolution has not ended. In fact, though the cosmical 

 problems which we have considered in their barest elements will not be 

 completely solved for centuries, it may be truly said that the questions 

 raised by the countless living organisms in a single drop of ditch water 

 are still more complex, and will require a still longer time for their solu- 

 tion. 



