DISPLACEMENT 



able material only, and no one would seriously 

 think of investing ether particles, which have no 

 weight, with inertia, which is based upon gravity 

 and in plain relation to mass. 



PROPOSITION XVII. 



A force continually passing from one ~body to 

 another body must be transmitted through a con- 

 tinuous flow of material from the transmitting body 

 to the receiving body. 



Let the circle S represent the sun. Let the circle 

 E represent the earth, and the dots between them 

 primary spheres. 



Let a force be transmitted from S to E through 

 the intervening primary spheres. Then the inter- 



vening bodies must undergo a change. (Prop. 

 XL) But the only change possible in primary 

 spheres is in their position (Prop. XIV.), and the 

 spheres join one another. (Prop. I.) 



If it be possible, let the force passing from S 

 move the first sphere nearest to S closer to the 

 second sphere. Then there is a vacancy between 



27 



