70 CLASSICS OF MODERN SCIENCE 



raised up to the orb of the moon, to be there compared with its body ; 

 if the weights of such bodies were to the weights of the external 

 parts of the moon as the quantities of matter in the one and in the 

 other respectively; but to the weights of the internal parts in a 

 greater or less proportion, then likewise the weights of those bodies 

 would be to the weight of the whole moon in a greater or less propor- 

 tion; against what we have showed above. 



Cor. I. Hence the weights of bodies do not depend upon their 

 forms and textures; for if the weights could be altered with the 

 forms, they would be greater or less, according to the variety of 

 forms in equal matter; altogether against experience. 



Cor. 2. Universally, all bodies about the earth gravitate towards 

 the earth ; and the weights of all, at equal distances from the earth's 

 centre, are as the quantities of matter which they severally contain. 

 This is the quality of all bodies within the reach of our experiments ; 

 and therefore (by rule 3) to be affirmed of all bodies what- 

 soever. ... 



Cor. 5. The power of gravity is of a different nature from the 

 power of magnetism ; for the magnetic attraction is not as the matter 

 attracted. Some bodies are attracted more by the magnet; others 

 less; most bodies not at all. The power of magnetism in one and 

 the same body may be increased and diminished ; and is sometimes 

 far stronger, for the quantity of matter, than the power of gravity; 

 and in receding from the magnet decreases not in the duplicate 

 but almost in the triplicate proportion of the distance, as nearly 

 as I could judge from some rude observations. 



BOOK III. PROPOSITION VII. THEOREM VII. 



That there is a power of gravity tending to all bodies, proportional 

 to the several quantities of fnatter which they contain. 



That all the planets mutually gravitate one towards another, we 

 have proved before ; as well as that the force of gravity towards every 

 one of them, considered apart, is reciprocally as the square of the dis- 

 tance of places from the centre of the planet. And thence (by prop. 

 69, book I, and its corollaries) it follows, that the gravity tending 

 towards all the planets is proportional to the matter which they 

 contain. 



