May 21, 1897.] 



SCIENCE. 



781 



through space, is made evident by a motion 

 of most of the stars in the opposite direction, 

 just as, passing through a country on a rail- 

 way, we see the houses on the right and on 

 the left being left behind us. It is clear 

 enough that the apparent motion will be 

 more rapid the nearer the object. We 

 may, therefore, form some idea of the dis- 

 tance of the stars when we know the 

 amount of the motion. It is found that, 

 in the great mass of stars of the sixth mag- 

 nitude, the smallest visible to the naked 

 eye, the motion is about three seconds per 

 century. As a measure thus stated does 

 not convey an accurate conception of 

 magnitude to one not practiced in the 

 subject, I would say that, in the heavens, 

 to the ordinary eye, a pair of stars will 

 appear single unless they are separated 

 by a distance of 150 or 200 seconds. Let 

 us then imagine ourselves looking at a 

 star of the sixth magnitude, which is at 

 rest while we are carried past it with the 

 motion of six or eight miles per second 

 which I have described. Mark its posi- 

 tion in the heavens as we see it to-day ; 

 then let its position again be marked 5,000 

 years hence. A good eye will just be 

 able to perceive that there are two stars 

 marked instead of one. The two would be 

 so close together that no distinct space be- 

 tween them could be perceived by unaided 

 vision. It is due to the magnifying power 

 of the telescope, enlarging such small ap- 

 parent distances, that the motion has been 

 determined in so small a period as the 150 

 yeai's during which accurate observations 

 of the stars have been made. 



The motion just described has been 

 fairly well determined for what astro- 

 nomically speaking are the brighter stars, 

 that is to say those visible to the naked 

 eye. But how is it with the millions 

 of faint telescopic stars, especially those 

 which form the cloud masses of the Milky 

 Way? The distance of these stars is 



undoubtedly greater, and the apparent 

 motion is, therefore, smaller. Accurate ob- 

 servations upon such stars have been com- 

 menced only recently, so that we have not 

 yet had time to determine the amount of 

 the motion. But the indication seems to 

 be that it will prove quite a measurable 

 quantity, and that before the twentieth cen- 

 tury has elapsed it will be determined for 

 very much smaller stars than those which 

 have heretofore been studied. A photo- 

 graphic chart of the whole heavens is now 

 being constructed by an association of ob- 

 servatories in some of the leading countries 

 of the world. I cannot say all the leading 

 countries, because then we should have to 

 exclude our own, which, unhappily, has 

 taken no part in this work. At the end of 

 the twentieth century we may expect that 

 the work will be repeated. Then, by com- 

 paring the charts, we shall see the effect of 

 the solar motion and, perhaps, get new 

 light upon the problem in question. 



Closely connected with the problem of 

 the extent of the universe is another which 

 appears, for us, to be insoluble because it 

 brings us face to face with infinity itself. 

 We are familiar enough with eternity, or, 

 let us say, the millions or hundreds of mil- 

 lions of years v/hich geologists tell us must 

 have passed while the crnst of the earth 

 was assuming its present form, our moun- 

 tains being built, our rocks consolidated, 

 and successive orders of animals coming 

 and going. Hundreds of millions of years 

 is, indeed, a long time, and yet, when we 

 contemplate the changes supposed to have 

 taken place during that time, we do not 

 look out on eternity itself, which is veiled 

 from our sight, as it were, by the unending 

 succession of changes that mark the prog- 

 ress of time. But in the motions of the 

 stars we are brought face to face with eter- 

 nity and infinity, covered by no veil what- 

 ever. It would bo bold to speak dogmat- 

 ically on a subject where the springs of 



