INTRODUCTION xvii 



But modem astronomy has done vastly 

 more than displace the habitation of man from 

 an assumed central position. It has given us 

 a view of the structure of the universe such 

 as was never dreamed of before. Not only is 

 the earth one of the smaller members of an 

 association of heavenly bodies travehng at 

 enormous speed around a centrally located 

 sun, but the whole solar system thus consti- 

 tuted, though its diameter is between five and 

 six thousand millions of miles, is small com- 

 pared with even the measurable space beyond 

 it. The star nearest to us is alpha centauri, 

 distant between four and five thousand times 

 the diameter of our system. Light from this 

 star takes over four years to reach us. No 

 means are known for measuring the distances 

 of the most remote stars. Some of them have 

 been estimated to be from seven to eight thou- 

 sand light-years from us ; that many of them 

 are removed by more than one hundred light- 

 years is certain. This distance amounts to 

 over one hundred thousand times the diame- 

 ter of our solar system and is unquestionably 

 far short of the actual distances of many stars. 

 None of us in this audience will live to see the 

 light which at this moment is starting toward 



