CHAPTER XXXV. 



THE SOLAR SYSTEM. 



GRAVITATION THE PLANETS SIZE AND MEASUREMENT OF THE 

 PLANETS SATELLITES FALLING STARS COMF.TS AEROLITES. 



GRAVITATION is the force which keeps the planets in their orbits, and this 



theory, perfected by Newton, was partially known to Kepler. Newton 



brought this idea into practical shape, and applied it mathematically. We 



know that every object in the world tends to attract every other object in 



proportion to the quantity of matter of which each consists. So the sun 



Fig. 526. Planets compared with a quarter of tne sun. 



attracts the planets, and they influence him in a minor degree. Likewise the 

 moon and our earth reciprocally attract each other. But as the sun's mass 

 is far greater than the masses of the planets he influences them more, and 

 could absorb them all without inconvenience or disturbance from his centre 

 of gravity. We have, in a former portion of this work, spoken of the law of 

 universal gravitation, which is the mutual attraction of any two bodtes to each 



