780 



SCIENCE. 



LN. S. Vol. V. No. 125. 



sibly the problem of these motions will be 

 the great one of the future astronomer. 

 Even now it suggests thoughts and ques- 

 tions of the most far-reaching character. 



I have seldom felt a more delicious sense 

 of repose than when crossing 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 ship to reach the star a Lyrse 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 Lyrse, 

 without its occurring to me that we are 

 actually making that very journey at a 

 speed compared with which the motion 

 of a steamship is slow indeed. Through 

 every year, every hour, every minute, 

 of human history from the first appear- 

 ance of man on the earth, from the era of 

 the builders of the Pyramids, through 

 the times of Caesar and Hannibal, 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 j ourney 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 cannot specify 

 more exactly than to say that it is probably 

 between five and nine miles per second. 

 We are at this moment thousands of miles 

 nearer to « Lyrse than we were a few 

 minutes ago when I began this discourse, 

 and through every future moment, for un- 

 told thousands of years to come, the earth 

 and all there is on it will be nearer to a 



Lyrse, 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 cannot 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 six or eight miles a 

 second can bring it about. 



I have called attention to this motion be- 

 cause it may, in the not distant future, 

 afford the means of approximating to a 

 solution of the problem already mentioned, 

 that of the extent of the universe. Ifot- 

 withstanding the success of astronomers 

 during the present century in measuring 

 the parallax of a number of stars, the most 

 recent investigations show that there are 

 very few, perhaps hardly more than a score 

 of stars of which the parallax, and there- 

 fore the distance, has been determined with 

 any approach to certainty. Many paral- 

 laxes, determined by observers about the 

 middle of the century, have had to disap- 

 pear before the powerful tests applied by 

 measures with the heliometer ; others have 

 been greatly reduced, and the distances of 

 the stars increased in proportion. So far as 

 measurement goes, we can only say of the 

 distances of all the stars, except the few 

 whose parallaxes have been determined, 

 that they are immeasurable. The radius of 

 the earth's orbit, a line more than ninety 

 millions of miles in length, not only van- 

 ishes from sight before we reach the dis- 

 tance of the great mass of stars, but becomes 

 such a mere point that, when magnified by 

 the powerful instruments of modern times, 

 the most delicate appliances fail to make it 

 measurable. Here the solar motion comes 

 to our help. This motion, by which, as I 

 have said, we are carried unceasingly 



