A HISTORY OF SCIENCE 



great change in the inner one. It is possible, how- 

 ever, that some of the observed changes may be due 

 to the existence of a resisting medium. If the changes 

 already suspected should be confirmed by repeated 

 observations with the same instruments, it will be 

 worth while to investigate more carefully whether 

 Saturn's rings are permanent or transitory elements 

 of the solar system, and whether in that part of the 

 heavens we see celestial immutability or terrestrial 

 corruption and generation, and the old order giving 

 place to the new before our eyes." 4 



Studies of the Moon 



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 mo- 

 ment 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 of 

 our planetary system, which the moon's misbehavior 

 had appeared to threaten. 



This highly satisfactory conclusion was an orthodox 

 belief of celestial mechanics until 1853, when Professor 

 Adams of Neptunian fame, with whom complex analy- 

 ses were a pastime, reviewed Laplace's calculation, 

 and discovered an error which, when corrected, left 

 about half the moon's acceleration unaccounted for. 



