22 THE PEOGEESS AND SPIEIT OF 



spheroidal figure of the earth itself. His suggestion that 

 the oblateness of the earth's spheroid might reciprocally be 

 determined by this irregularity of the moon's motion led 

 Burg to a calculation, the results of which closely tallied with 

 the best measurements and pendulum observations. Very 

 recently new and more delicate causes 6f lunar disturbance 

 have been indicated, as depending on the action of the planet 

 Venus ; first, indirectly, by its perturbing the motion of the 

 earth, altering our distance from the sun, and thereby affect- 

 ing the motion and position of the moon during periods of 

 120 years ; secondly, by a minute disturbance arising from 

 the direct action of Venus on the moon itself. In all these 

 cases the theory accords with the phenomena observed ; and 

 this accordance well illustrates the perfection of use which 

 the great law of gravitation has now attained. 



In passing the bounds of our own system narrow^ we 

 may call them, in relation to what lies beyond we lose in 

 great part the guidance of this law ; though retaining such 

 proof of its equal and probably similar operation in the most 

 distant regions of space, as almost to force upon us the 

 conclusion (warranted indeed by other considerations) that 

 Motion is universal and constant in all matter that nothing 

 in the universe around us is at absolute rest. To prove the 

 continuous movement of the solar system in space, with the 

 direction and rate of its motion ; to confirm this wonderful 

 fact by the discovery of the proper and absolute motions of 

 other stars; to determine by parallactic observations of 

 incredible delicacy the distances of certain of the fixed stars, 

 and to measure these distances by the years which light 

 takes to traverse them; to demonstrate, among the many 

 thousand double or multiple stars now discovered, those orbits 

 and periods of revolution which obey the same law that 

 brought Newton's apple to the ground ; to gauge by refined 

 processes our own nebula of the Milky Way ; to discover 



