THE STORY OF NINETEENTH-CENTURY SCIENCE 



father's double stars. His studies, in which at first he had 

 the collaboration of Mr. James South, brought to light 

 scores of hitherto unrecognized pairs, and gave fresh 

 data for the calculation of the orbits of those longer 



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known. So also did the independent researches of F. 

 G. W. Struve, the enthusiastic observer of the famous 

 Russian observatory at the university of Dorpat, and 

 subsequently at Pulkowa. Utilizing data gathered by 

 these observers, M. Savary of Paris showed in 1827 that 

 the observed elliptical orbits of the double stars are ex- 

 plicable by the ordinary laws of gravitation, thus con- 

 firming the assumption that Newton's laws applv- to 

 these sidereal bodies. Henceforth there could be no 

 reason to doubt that the same force which holds terres- 

 trial objects on our globe pulls at each and every par- 

 ticle of matter throughout the visible universe. 



The pioneer explorers of the double stars early found 

 that the systems into which the stars are linked are by 

 no means confined to single pairs. Often three or four 

 stars are found thus closely connected into gravitation 

 systems ; indeed, there are all gradations between bi- 

 nary systems and great clusters containing hundreds or 

 even thousands of members. It is known, for example, 

 that the familiar cluster of the Pleiades is not merely 

 an optical grouping, as was formerly supposed, but an 

 actual federation of associated stars, some 2500 in num- 

 ber, only a few of which are visible to the unaided eye. 

 And the more carefully the motions ot the stars are 

 studied, the more evident it becomes that wideh 7 sepa- 

 rated stars are linked together into infinitely complex 

 systems, as yet but little understood. At the same time 

 all instrumental advances tend to resolve more and more 

 seemingly single stars into close pairs and minor clus- 



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