CHAPTERS ON THE STARS. 23 1- 



mining their motions, might be considered as, after all, barren of 

 results of the highest human interest. When we know the exact 

 position of every star in the heavens, the direction in which it is 

 moving and the character of its spectral lines, how much wiser are we? 



What could hardly have been foreseen fifty years ago, is that these 

 various classes of results are now made to combine and converge upon 

 the greatest problem which the mind of man has ever attempted to 

 grasp — that of the structure of the universe. The study of variable 

 stars has suddenly fallen into line, so to speak, so that now, it is uniting 

 itself to the study of all the other subjects to give us at least a faint 

 conception of what the solution of this problem may be. 



One of the principal objects of the present chapter is to make a 

 comparison of these various researches, and discuss the views respect- 

 ing the constitution of the stars individually, as well as of the universe 

 as a whole, to which they lead us. But there are a number of details 

 to be considered singly before we can combine results in this way. Our 

 early chapters will therefore be devoted to the special features and 

 individual problems of stellar astronomy which have occupied the minds 

 of astronomers from the beginning of their work to the present time. 

 Keeping these details in mind, we can profitably proceed to the con- 

 sideration of the general conclusions to be drawn from them. 



We may begin by refreshing our memories on some points, an 

 understanding of which must be taken for granted. What are famil- 

 iarly known as the heavenly bodies belong to two classes. Those nearest 

 to us form a sort of colony far removed from all the others, called the 

 solar system. The principal bodies of this system are the sun and 

 eight great planets with their moons, revolving round it. On one 

 of the planets, small when compared with the great bodies of the uni- 

 verse, but large to our every-day conceptions, we dwell. The other 

 planets appear to us as stars. Four of them, Venus, Mars, Jupiter 

 and Saturn, are distinguished from the fixed stars by their superior 

 brightness and characteristic motions. Of the remaining three, Mer- 

 cury will only rarely excite notice, while Uranus and Neptune are as 

 good as invisible to the naked eye. 



The dimensions of the solar system are vast when compared with 

 any terrestrial standard; A cannon shot going incessantly at its utmost 

 speed would be a thousand years in crossing the orbit of Neptune from 

 side to side. But vast as the dimensions are, they sink into insignifi- 

 cance when compared with the distance of the stars. Outside the solar 

 system are spaces which, so far as we know, are absolutely void, save 

 here and there a comet or a meteor, until we look far outside the region 

 which a cannon shot would cross in a million of years. 



The nearest star is thousands of times farther away than the most 

 distant planet. Scattered at these inconceivable distances are the bodies 



