

GRAVITATION 12 i 



sion of the tendency to be drawn to the center of the earth. 

 Every particle of matter has this tendency. The denser 

 an object is, the greater its number of molecules and, 

 hence, the greater its weight. 



At the poles of the earth, the distance to the center of 

 the earth is less than at the equator. Hence, an object, 

 according to Newton's law, at one of the poles should 

 weigh less than the same object at the equator. Actual 

 measurements show this to be the case. 



We must not forget that this law of mass attraction 

 works both ways. That is, the smaller object attracts 

 the greater as well as the greater the smaller, though the 

 only visible effect may be the effect on the smaller object. 

 The level of the ocean along the west coast of South America 

 has been found to be higher than its level at other places. 

 This is believed to be due to the mass attraction of the 

 huge range of the Andes Mountains. The attraction 

 of the earth as a whole tends to keep the oceans at the 

 same level, but the mass of the Andes above the water- 

 level is sufficiently great to cause in its neighborhood a 

 measurable variation of that level. 



Why does oil ascend the wick of a candle? This is 

 due, at least in part, to the effect of the mass attraction 

 of the wick upon the molecules of oil. 



Note that the explanation of facts by the law of gravita- 

 tion is a very different thing from explaining gravitation. 

 That is a thing which no one has explained. This is one 

 of those great laws of nature which, in elementary work 

 at least, we do not attempt to explain. We simply call 

 these laws causes and seek to see the connection between 

 such causes and their e/ects. It is very important to 

 realize that given causes do inevitably produce certain 



