136 LECTURES 



We may also give a partial answer to the question, how far oif may a 

 star be seen ? Photometric measurements, deemed reliable, show that 

 Sirius would be as bright as an ordinary star of the sixth magnitude 

 at ten times its present distance ; the light would then be 220 years 

 in coming to us. But Sir John Herschel's twenty-foot reflector, and 

 still more the great telescope of Lord Rosse, would bring out a star of 

 the sixth magnitude at seventy-five times its present distance. Hence 

 Sirius might be seen at 750 times the distance which now intervenes 

 between it and us. To traverse so vast a space light would require 

 the long period of 16,500 years ! But why should we stop here? No 

 law of the universe bars our progress. And yet, again, what were 

 the use of attempting to advance farther ? The steps become so vast 

 that we hesitate to take them. We labor under the oppressive convic- 

 tion that, if millions of them were taken, we reach no end. There is 

 every presumption in favor of the hypothesis — nay, there is positive 

 inductive reason for believing, that, from groups of stars and nebulfe, 

 light reaches the human eye which has been 100,000 years in its tire- 

 less flight from the distant verge of the universe. 



From what we now know, can we then doubt that the stars which 

 beam efFulgently upon us, or merely twinkle from the serene depths 

 of ether, are great central suns ? Nay, that many of them are great 

 central suns, far surpassing our own in their intrinsic splendor? 

 Wollaston has shown, by photomdiscal measurements, in Herschel's 

 opinion, " apparently unobjectionable," that the intrinsic splendor of 

 a Centauri is equal to nearly 2^ suns, and that Sirius is probably equal 

 to 63 suns. Such is the vastuess and the grandeur of the starry heavens. 

 We look upon the millions of those brilliant orbs, which, scattered 

 through illimitable space, light up the universe of God, and these 

 are but parts of His works ! What, then, do they tell us of time and 

 space, of infinite intelligence, and omnipotent power ! Well might 

 we ask with the patriarch, "canst thou by searching find out God unto 

 perfection?" 



There is one other topic to which I shall briefly allude, it is that of 

 double stars. We here speak of stars connected together so as to form 

 a system, not of those which are only optically double, in consequence 

 of the two being nearly in the same direction. Of the double stars, 

 which evidently form systems of their own, some are binary, consist- 

 ing of two stars ; some triple, and others, perhaps, quadruple. 



Sir William Herschel was the first to recognize the importance of 

 this particular branch of stellar astronomy, and the first to enter upon 

 it. He made a catalogue of 500 double stars, which were suspected 

 to have motions of revolution about each other. Since his time the 

 catalogue, by the labors of Struve, Peters, and others, has been 

 extended to 3,000. Two observed elements indicate amotion of revo- 

 lution of two stars, the one about the other, or both about their com- 

 mon centre of gravity. The first is a variation of the angular distance 

 between them, and the second is a progressive rotary movement in the 

 line joining them. Both these elements of position can be observed 

 with great precision. The first will tend to develop the form of the 

 orbit, the second the time of revolution. If the plane of the stellar 

 orbit should chance to be perpendicular to the visual ray, we shall see 



