From: fortunati.luigi@gmail.com   
      
   Newton's formula F=GmM/d^2 has been used to great advantage so far   
   because it has proven to be valid and almost perfectly correct except   
   for the small discrepancy in the perihelion calculation of Mercury's   
   orbit, where Einstein's gravity formulas prove to be more precise.   
      
   So, Newton's formula is *almost* correct but not quite.   
      
   In this formula, the force is proportional to the product of the two   
   masses (m*M).   
      
   Suppose that body A has mass M=1000 and body B has mass m=1, so that   
   the force between the two bodies is proportional to 1000 (mM=1*1000).   
      
   If another unit mass 1 is added to body B, its mass doubles to m=2 and   
   the force acting between the two bodies also doubles, because it will   
   be proportional to 2000 (mM=2*1000).   
      
   But if the other unit mass is added to body A (instead of body B) the   
   mass of A will become equal to M=1001 (remaining almost unchanged) just   
   as the force between the two bodies remains practically unchanged and   
   will be proportional to 1001 (mM=1*1001).   
      
   Why does the force acting between the two bodies double if we add the   
   unit mass to body B and, substantially, does not change if we add it to   
   the mass of body A?   
      
   Luigi Fortunati   
      
   --- SoupGate-DOS v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)