THE WONDERFUL CENTURY. 



vestigation, proved that either solid or liquid rings would 

 be unstable, and would inevitably break up so as to form 

 a number of satellites; and he concluded that the rings 

 really consisted of a crowd of small bodies so near to- 

 gether as to appear like a solid mass; and as the appear- 

 ance of the rings, and some slight changes detected in 

 them, were in harmony with this view, it has been gen- 

 erally accepted. But quite recently the wonderful in- 

 strument, the spectroscope, has given the final demon- 

 stration that this theory is correct. If the rings are 

 solid, it is clear that a point on the outer edge must move 

 more rapidly than one on the inner edge; whereas, if 

 they consist of separate particles, each revolving inde- 

 pendently round the planet, then, in accordance with 

 the laws of all planetary motions, those forming the 

 inner side of the rings, being nearer to the planet, must 

 move much quicker than those on the outer side. As 

 already explained in Chapter VI., the spectroscope 

 enables us to measure motion in the line of sight that 

 is, toward or away from us of any heavenly bodies, 

 and by observing the outer extremities of the rings to 

 the right and left of the planet, where the motion is, of 

 course, in these two directions, it is found that the mo- 

 tion of the inner edge is considerably more rapid than 

 that of the outer edge, showing that those parts move 

 round the planet independently, and are therefore 

 formed of separate particles or small masses. These 

 observations were made by the American astronomer, 

 Professor James E. Keeler, in 1895, and are of extreme 

 delicacy; but that they are trustworthy is shown by the 

 fact that the resulting velocities are in accordance with 

 Kepler's third law, which determines the relative mo- 



