THE CENTURY'S PROGRESS IN ASTRONOMY 



on its frigid way eight thousand years before it could 

 reach the very nearest of our neighbor stars ; and even 



t Cj 7 



then it would have penetrated but a mere arm's-length 

 into the vistas where lie the dozen or so of sidereal resi- 

 dents that are next beyond. Even to the trained mind 

 such distances are only vaguely imaginable. Yet the 

 astronomer of our century has reached out across this 

 unthinkable void and brought back many a secret 

 which our predecessors thought forever beyond human 

 grasp. 



A tentative assault upon this stronghold of the stars 

 was being made by Herschel at the beginning of the 

 century. In 1802 that greatest of observing astrono- 

 mers announced to the Eoyal Society his discovery that 

 certain double stars had changed their relative positions 

 towards one another since he first carefully charted 

 them twenty years before. Hitherto it had been sup- 

 posed that double stars were mere optical effects. Now 

 it became clear that some of them, at any rate, are true 

 " binary systems," linked together presumably by gravi- 

 tation, and revolving about one another. Halley had 

 shown, three-quarters of a century before, that the stars 

 have an actual or "proper" motion in space; Herschel 

 himself had proved that the sun shares this motion with 

 the other stars. Here was another shift of place, hith- 

 erto quite unsuspected, to be reckoned with by the as- 

 tronomer in fathoming sidereal secrets. 



When John Herschel, the only son and the worthy 

 successor of the great astronomer, began star-gazing in 

 earnest, after graduating senior wrangler at Cambridge, 

 and making two or three tentative professional starts in 

 other directions to which his versatile genius impelled 

 him, his first extended work was the observation of his 



63 



