THE STORY OF NINETEENTH-CENTURY SCIENCE 



the Harvard observatory, in America, and the Rev. 

 W. R. Dawes in England, was another interesting op- 

 tical achievement ; but our most important advances 

 in knowledge of Saturn's unique system are due to the 

 mathematician. Laplace, like his predecessors, supposed 

 these rings to be solid, and explained their stability as 

 due to certain irregularities of contour which Herschel 

 had pointed out. But about 1851 Professor Peirce of 

 Harvard showed the untenability of this conclusion, 

 proving that were the rings such as Laplace thought 

 them, they must fall of their own weight. Then Pro- 

 fessor J. Clerk Maxwell of Cambridge took the matter 

 in hand, and his analysis reduced the puzzling rings to a 

 cloud of meteoric particles a " shower of brickbats " 

 each fragment of which circulates exactly as if it were 

 an independent planet, though of course perturbed and 

 jostled more or less by its fellows. Mutual perturbations, 

 and the disturbing pulls of Saturn's orthodox satellites, 

 as investigated by Max-well, explain nearly all the phe- 

 nomena of the rings in a manner highly satisfactory. 



But perhaps the most interesting accomplishments of 

 mathematical astronomy from a mundane stand-point, 

 at any rate are those that refer to the earth's own 

 satellite. That seemingly staid body was long ago 

 discovered to have a propensity to gain a little on the 

 earth, appearing at eclipses an infinitesimal moment 

 ahead of time. Astronomers were sorely puzzled by 

 this act of insubordination ; but at last Laplace and 

 Lagrange explained it as due to an oscillatory change in 

 the earth's orbit, thus fully exonerating the moon, and 

 seeming to demonstrate the absolute stability and per- 

 manence of our planetary system, which the moon's 

 misbehavior had appeared to threaten. 



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