IDENTICAL CHANGES 



PROPOSITION V. 



Force cannot be transmitted between two bodies 

 in opposite directions at the same time. 



Let Figure A represent two bodies, B and C, and 

 let D represent a rod between them. 



Then it would be absurd to suppose that force 

 can move the rod in the direction from B to C, at 

 the same time that force is moving the rod in the 

 direction from C to B. 



Yet it is sometimes held that a body receiving 

 light or heat, from another body, does at the same 

 time give to the body from which it received. 



And the explanation involves some theory of 

 force which divorces force and matter, for no wave 

 even may go opposite directions at once. Because 

 force always acts through the medium of material, 

 and no material may go two opposite ways at 

 the same time ; therefore, force cannot be transmit- 

 ted between two bodies in opposite directions at the 

 same time. 



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