Scientific Lectures. 273 



4,000 years, that is witliiii a period no longer tlian over wliicli human 

 history extends. 



And noAV, what is this sun of ours — this center round which eight 

 large planets, with not less than eighteen satellites and one hundred 

 and nine small planets, are known to revolve, besides comets unnum- 

 bered and countless swarms of meteors ; this luminary, whose fervent 

 and dazzling beams radiate and have radiated for ages with a pro- 

 fusion which has shown no signs of failing, although the most vehe- 

 ment combustion fails to equal it in heat, and the most intense elec- 

 trical action falls short of it in light ; which, notwithstanding the enor- 

 mous floods of energy which it is pouring out, has decreased neither 

 in weight nor size to any extent which human skill has sufficed to 

 detect ? And does the realm of nature show any other object com- 

 parable with it in magnitude or in character ? These are among the • 

 questions which force themselves on our consideration. 



The sun is a star, apparently not unlike the most of those which 

 gem the sky by night. This seems a better statement than to say 

 that the stars are suns, although it would be difficult to give a good 

 definition for either word. Our idea of a sun seems to imply that it 

 is a center for a system of planets or satellites, dependent upon it 

 for their light and radiant heat. There is some ground for believing 

 this to be the case with some of the fixed stars, but for supposing it 

 to be 80 with most of them there is no reason other than the supposed 

 analogy ; but that the sun is a star, one of the same great company 

 which spangle the firmament, and indeed, one of the countless myri- 

 ads which compose the single nebula which we see all around us like 

 a ring and call the milky way, seems a well established fact. Here, 

 as witli them, that same law of gravitation holds unrestricted sway, 

 which the double stars reveal to us as the guide and cor^~iroller of 

 their motions. Like many of them, it is variable in its light, 

 although only to a small extent, and with a long period. Like them 

 it is journeying througli space, drawn by some powerful attraction, 

 or performing a stupendous orbit around some center whicli astrono- 

 mers have not yet succeeded in recognizing. Its annual motion has 

 been computed by Otto Struve to be 150,000,000 miles. 



And, notwithstanding its awful magnitude, we must still regard 

 the sun as a comparatively small star, at least as not above the ave- 

 rage size. This is proved by comparing his light with that of the 

 very few fixed stars whose distance can be computed, and can there- 

 fore be compared with that of the sun. 

 [Inst.] 18 



