166 ANNUAL REPORT SMITHSONIAN INSTITUTION, 192 8 



For in all probability the life in front of the human race must 

 enormously exceed the short life behind it. A million million years 

 hence, so far as we can foresee, the sun will probably still be much as 

 now, and the earth will be revolving round it much as now. The 

 year will be a little longer, and the climate quite a lot colder, while 

 the rich accumulated stores of coal, oil, and forest will have long 

 been burned up; but there is no reason why our desendants should 

 not still people the earth. Perhaps it may be unable to support so 

 large a population as now, and perhaps fewer will desire to live on 

 it. On the other hand, mankind, being three million times as old 

 as now, may— if the conjecture does not distress our pessimists too 

 much — be three million times as wise. 



Looked at on the astronomical time scale, humanity is at the very 

 beginning of its existence — a newborn babe, with all the unexplored 

 potentialities of babjdiood ; and until the last few moments its interest 

 has been centered, absolutely and exclusively, on its cradle and feeding 

 bottle. It has just become conscious of the vast world existing out- 

 side itself and its cradle; it is learning to focus its eyes on distant 

 objects, and its awakening brain is beginning to wonder, in a vague, 

 dreamy way, what they are and what purpose they serve. Its interest 

 in this external world is not much developed yet, so that the main 

 part of its faculties is still engrossed with the cradle and feeding 

 bottle, but a little corner of its brain is beginning to wonder. 



Taking a very gloomy view of the future of the human race, let 

 us suppose that it can only expect to survive for 2,000 million years 

 longer, a period about equal to the past age of the earth. Then, re- 

 garded as a being destined to live for threescore years and ten, hu- 

 manity, although it has been born in a house 70 years old, is itself 

 only 3 days old. But only in the last few minutes has it become con- 

 scious that the whole world does not center round its cradle and its 

 trappings, and only in the last few ticks of the clock has any adequate 

 conception of the size of the external world dawned upon it. 



For our clock does not tick seconds, but years; its minutes are the 

 lives of men. A minute and a half ago the distance of a star was 

 jBrst measured and provided a measuring rod for the universe. A 

 quarter of a minute ago, Hertzsprung and Shapley showed how the 

 peculiar stars known as Cepheid variables provide a longer measuring 

 rod, and taught us to think in distances so great that light takes 

 hundreds of thousands of years to traverse them. With the very 

 last tick of the clock, Hubble, using the same measuring rod, has 

 found that the most remote objects visible in the biggest telescope on 

 earth are so distant that light, traveling 186,000 miles a second, takes 

 about 140 million years to come from them to us. 



Not only is our vision of the universe continually expanding, but 

 also it is expanding at an ever-increasing rate. Is this expansion des- 



