6 THE BODIES OF SPACE, 



poles, as a consequence of rotation on an axis when in a soft 

 state, for the same reason that a mass of clay whirled rapidly 

 round will become of a similar shape. The sun and earth are 

 mutually attracted in proportion to their respective masses, 

 and inversely as the square of the distance, which is a law 

 prevailing with not less certainty upon two rose leaves floating 

 on the summer lake into which they have fallen. The revolu- 

 tion of the planet or satellite in an orbit round a central mass 

 is, again, the result of a composition of two opposite forces 

 one of them this attraction of gravity in its proper proportions, 

 the other a primitive motion of the one mass away from the other 

 in a straight line ; and this phenomenon is exemplified when 

 we see a stone which has been thrown from a boy's hand, 

 brought in a curve to the ground. All these marvels rest on 

 mathematical calculations of the nicest exactness, insomuch 

 that, taking one as an example, astronomers have computed 

 ten years beforehand, the time at which the planet Jupiter 

 would pass our meridian, and the predicted time was correct 

 within half a second. 



Since Newton stated the laws of gravity and of the plane- 

 tary motions, there have been some important additions to his 

 philosophy. It has been shown, that certain perturbations in 

 the planetary movements, which appeared to him as denoting 

 a necessary end to the system, observe periods, and are only 

 further proofs of the stability of the whole arrangement. It 

 has also been discovered that the laws of motion extend be- 

 yond the solar system. Amongst the orbs, which seem so still 

 and serene to our ordinary perceptions, we now know that 

 there is no such thing as rest. Stars are ascertained to have 

 proper motions, of the same nature with that found in our 

 own sun. Many are seen to be, in reality, double or triple 

 that is, composed of a plurality of suns, which perform regular 

 revolutionary motions round each other in ellipses. The 

 periods of some of these movements and revolutions are of 

 such brevity, that their elements are already in the book of 

 the astronomer ; others are seen to be of such vastness, that 

 the times which have determinated the youth and death of our 

 oldest empires, would be, in comparison, but as a little spoke 

 in some enormous wheel. Yet of all of them no doubt can be 

 entertained that they depend upon those simple physical laws 

 which preside over every particle of tangible matter in our 

 own sphere. 



Here it is right to advert to some general features of the 



