256 NEWTON S PRINCIPIA. 



certain astherial medium extremely rare, which freely 

 pervades the pores of all bodies, and from such a medium 

 some resistance must needs arise, in order to try whether 

 the resistance which we experience in bodies in mo 

 tion be made upon their outward superficies only, or 

 whether their internal parts meet with any considerable 

 resistance upon their superficies, I thought of the follow 

 ing experiment.&quot; Newton suspended a round deal box by 

 a thread 11 feet long, and compared the resistance made 

 to it when empty and when filled with lead. When full 

 of air its weight was ^ ih of the weight when filled with 

 metal. But since the decrement of the arc varies in 

 versely as the weight, the box when filled with lead should 

 make 78 oscillations before the arc was decreased by the 

 same quantity that when filled with air it lost in one 

 oscillation. But New ton counted 77 oscillations. Assuming 

 that the greater resistance of the full box arises not from 

 any other latent cause, but only from the action of some 

 subtile fluid on the included metal, we may suppose that 

 this resistance in equally swift bodies will be as the num 

 ber of particles that are resisted. Let A be the resistance 

 on the external and B on the internal superficies of the 

 box when empty. Then A and 78 B will be these re 

 sistances when the box is full. By the preceding ex 

 periment the resistance on the full box A + *78B is to the 

 resistance on the empty box A B as 78 to 77. Solving 

 this simple equation, it follows that the resistance on the 

 internal parts of the empty box {B) will be j-gg-^ P art 

 of the resistance (^4) on the external superficies. 



