86 THE PROBLEMS OF ASTRONOMY. 



On some aspects of the problem of the extent of the universe light 

 is being - thrown even now. Evidence is gradually accumulating which 

 points to the probability that the successive orders of smaller and 

 smaller stars, which our continually increasing telescopic power brings 

 into view, are not situated at greater and greater distances, but that 

 we actually see the boundary of our universe. This indication lends a 

 peculiar interest to various questions growing out of the motions of the 

 stars. Quite possibly the problem of these motions will be the great 

 one of the future astronomer. Even now it suggests thoughts and 

 questions of the most far-reaching character. 



I have seldom felt a more delicious sense of repose than when cross- 

 ing the ocean during the summer months I sought a place where I 

 could lie alone on the deck, look up at the constellations, with Lyra 

 near the zenith, and, while listening to the clank of the engine, try to 

 calculate the hundreds of millions of years which would be required by 

 our skip to reach the star a Lyrae if she could continue her course in 

 that direction without ever stopping. It is a striking example of how 

 easily we may fail to realize our knowledge when I say that I have 

 thought many a time how deliciously one might pass those hundred 

 millions of years in a journey to the star a Lyrre, without its occurring 

 to me that we are actually making that very journey at a speed com- 

 pared with which the motion of a steamship is slow indeed. Through 

 everjr year, every hour, every minute, of human history from the first 

 appearance of man on the earth, from the era of the builders of the 

 Pyramids, through the times of Csesar and Ilannibal, through the period 

 of every event that history records, not merely our earth, but the sun 

 and the whole solar system with it, have been speeding their way 

 toward the star of which I speak on a journey of which we know neither 

 the beginning nor the end. During every clock beat through which 

 humanity has existed it has moved on this journey by an amount which 

 we can not specify more exactly than to say that it is probably between 



5 and 9 miles per second. We are at this moment thousands of 

 miles nearer to a Lyrse than we were a few minutes ago when I began 

 this discourse, and through every future moment, for untold thousands 

 of years to come, the earth and all there is on it will be nearer to a 

 Lyra?, or nearer to the place where^that star now is, by hundreds of 

 miles for every minute of time come and gone. When shall we get 

 there % Probably in less than a million years, perhaps in half a million. 

 We can not tell exactly, but get there we must if the laws of nature 

 and the laws of motion continue as they are. To attain to the stars 

 was the seemingly vain wish of the philosopher, but the whole human 

 race is, in a certain sense, realizing this wish as rapidly as a speed of 



6 or 8 miles a second can bring it about. 



I have called attention to this motion because it may, in the not dis- 

 tant future, afford the means of approximating to a solution of the 

 problem already mentioned — that of the extent of the universe. Not- 



