May 21, 1897.] 



SCIENCE. 



779 



the visible universe. How far does this 

 universe extend? What are the distances 

 and arrangements of the stars ? Does the 

 universe constitute a system ? If so, can we 

 comprehend the plan on which this system is 

 formed, of its beginning and of its end ? 

 Has it bounds outside of which nothing 

 exists but the black and starless depths of 

 infinity itself? Or are the stars we see 

 simply such members of an infinite collec- 

 tion as happen to be the nearest our sys- 

 tem ? A few such questions as these we are 

 perhaps beginning to answer ; but hundreds, 

 thousands, perhaps even millions of years 

 may elapse without our reaching a complete 

 solution. Yet the astronomer does not 

 view them as Kantian antinomies, in the 

 nature of things insoluble, but as ques- 

 tions to which he may hopefully look for at 

 least a partial answer. 



The problem of the distances of the stars 

 is of peculiar interest in connection with 

 the Copernican system. The greatest ob- 

 jection to this system, which must have 

 been more clearly seen by astronomers 

 themselves than by any others, was found 

 in the absence of any apparent parallax of 

 the stars. If the earth performed such an 

 immeasurable circle around the sun as 

 Copernicus maintained, then, as it passed 

 from side to side of its orbit, the stars out- 

 side the solar system must appear to have a 

 corresponding motion in the other direction, 

 and thus to swing back and forth as the earth 

 moved in one and the other direction. The 

 fact that not the slightest swing of that sort 

 could be seen was, from the time of Ptolemy, 

 the basis on which the doctrine of the 

 earth's immobility rested. The difiiculty 

 was simply ignored by Copernicus and his 

 immediate successors. The idea that Na- 

 ture would not squander space by allowing 

 immeasurable stretches of it to go unused 

 seems to have been one from which medise- 

 val thinkers could not entirely break away. 

 The consideration that there could be no 



need of any such economy, because the sup- 

 ply was infinite, might have been theoret- 

 ically acknowledged, but was not practically 

 felt. The fact is that magnificent as was the 

 conception of Copernicus, it was dwarfed by 

 the conception of stretches from star to star 

 so vast that the whole orbit of the earth was 

 only a point in comparison. 



An indication of the extent to which the 

 difiiculty thus arising was felt is seen in 

 the title of a book published by Horre- 

 bow, the Danish astronomer, some two 

 centuries ago. This industrious observer, 

 one of the first who used an instrument 

 resembling our meridian transit of the 

 present day, determined to see if he 

 could find the parallax of the stars by ob- 

 serving the intervals at which a pair of 

 stars in oppposite quarters of the heavens 

 crossed his meridian at opposite seasons of 

 the year. When, as he thought, he had won 

 success he published his observations and 

 conclusions under the title of ' Copernicus 

 Triumphans.' But alas! the keen criticism 

 of his contemporaries showed that what he 

 supposed to be a swing of the stars from 

 season to season arose from a minute varia- 

 tion in the rate of his clock, due to the dif- 

 ferent temperatures to which it was exposed 

 during the day and the night. The mea- 

 surement of the distance even of the near- 

 est stars evaded astronomical research, un- 

 til Bessel and Struve arose in the early part 

 of the present century. 



On some aspects of the problem of the ex- 

 tent of the universe light is being thrown 

 even now. Evidence is gradually accumu- 

 lating which points to the probability that 

 the successive orders of smaller and smaller 

 stars, which our continually increasing tele- 

 scopic 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 pecu- 

 liar interest to various questions growing 

 out of the motions of the stars. Quite pos- 



