OF SOLIDS AND LIQUIDS. 237 



the centre of the earth, are as the quantities of 

 matter in the bodies : this is collected from the 

 equal acceleration of all bodies, that fall from 

 a state of rest, by the force of their weights ; 

 for the forces, by which unequal bodies are 

 equally accelerated, must be proportional to the 

 quantities of matter to be moved. Now that 

 all bodies are in falling equally accelerated, ap- 

 pears from hence, that when the resistance of 

 the air is taken away, as it is under an ex- 

 hausted receiver, bodies falling describe equal 

 spaces, in equal times." 



The equal distances which bodies describe 

 in equal times, whose densities are altogether 

 unequal, evidently prove, that weight and mo- 

 tion are different from each other ; and that the 

 acceleration of motion, in falling bodies, de- 

 pends more on the nature of the medium in 

 which they are placed, than on the abstract 

 quantity of matter which they contain ; hence 

 it is, that a feather and a guinea, a rare and a 

 dense body, placed in an exhausted receiver, 

 are found to fall from equal heights, in equal 

 times. The weight of a body, and the motion 

 of a body, do not, therefore, altogether depend 

 on the quantity of matter in each ; we may 

 consequently infer, that this accelerated motion 

 which dense bodies acquire, in their passage 

 from great heights, through rare media, depends 

 more on the difference which exists between 



