428 RISE AND PROGRESS OF 



wonder to the learned. Newton immediately perceived in it a 

 new effect of gravitation : he proved that the earth itself, sup- 

 posing it to be fluid and homogeneous, would assume the form of 

 an oblate spheroid, whose greatest and least diameters are in the 

 ratio of 230 to 229 ; and that the force of gravity must increase 

 from the equator to the poles, the increment being proportional to 

 the square of the sine of latitude. The attraction of the sun and 

 moon upon the redundant matter encompassing the equatorial 

 parts of the earth was shown to account for the precession of the 

 equinoxes. The phenomena of the tides were proved to arise from 

 the same actions, exerted upon the waters of our ocean ; and 

 from a comparison of the effects produced at spring and neap 

 tides (when these two forces conspire or are opposed) Newton 

 deduced the proportion of the forces, and thence determined 

 approximately the mass of the moon, and even its density, as 

 compared with the earth. 



This last result is certainly one which cannot fail to strike the 

 uninstructed with wonder. That the mathematician should be 

 enabled to weigh the moon's mass, and even to compute its 

 density, from its effects upon the waters of our sea, is indeed 

 truly wonderful ; but it is only one of many results of the same 

 nature reached by Newton in following out the great principle of 

 universal gravitation. By comparison of the orbit of the moon 

 round the earth with that of the earth round the sun, the mass 

 of the earth (relatively to that of the sun) is at once determined ; 

 and the same principles are applicable to all the planets which 

 are attended by satellites. 



Such are among the more prominent discoveries developed in 

 the Principia of Newton. Its concluding pages are dedicated to 

 the proofs, which the laws of the material world afford, of the 

 existence and attributes of the great First Cause. This is as it 

 should be : and while we admire the genius of the man who could 

 penetrate so far into nature's mysteries, and bind all these varied 

 and complicated phenomena by a single tie, our thoughts are 

 insensibly raised from the creature, to whom it was permitted to 

 gain so large an insight into this wondrous work, to the Infinite 

 Intelligence that planned the whole, and the Infinite Power that 

 called it into being. 



)f the advances which mechanical science has made, since the 

 time of Newton, I must speak but briefly. The first great step 



