ON ASTEONOMY. 



137 



it developed in its true form If that plane should coincide with the 

 visual ray, then, whatever the real form of the orbit, it would appear 

 to us to be a straight line. The com[)anion would make a transit 

 across the principal star, or be occulted by it every serai-revolution. 

 It is now well known that, in the binary systems, the stars revolve in 

 elliptical orbits. Of this class Sir John Herschel gives a catalogue of 

 15, in which the periodic times and tlie forms of the orbits have been 

 proximately determined. The periodic times vary from 31 to *736 

 years, y Leonis, not included in his catalogue, indicates a period of 

 1,200 years. Of these stars, some have completed more than a revo- 

 lution since their orbits were computed. One of the most interesting 

 of the double stars is y Virginis. The companion passed the peri- 

 helion of its orbit in 1836, when no telescope in Europe could sepa- 

 rate the two. The periodic time is 182 years, the major axis 3". 5, the 

 orbit very elliptical. 



Fig. 21 gives a view of the re- ^ » 



spective positions of the companion 

 from 1830 to 1844. 



These orbits of the double stars 

 furnish the most conclusive evi- 

 dence that the law of gravitation 

 controls the movement of the most 

 distant stars no less than the orbits 

 of the component members of our 

 own system. It is truly and em- 

 phatically the law of universal 

 gravitation, and binds together, in 

 the strictest sense, the material 

 universe of God. 



Such are the methods by which 

 we ascend to the vast heights of sidereal astronomy, and such are the 

 lofty conceptions which it gives us of the works and attributes of the 

 Great Creator. 



