Consider the force of a macrodipole produced by a dielectric boundary.

It is NOT zero, but rather twice the force of each charge on the dipole.

The limit as the size of the macrodipole is made smaller is undetermined
until the details of the limiting process are specified. If the dipole is made 
infinitely small, and then the force is calculated, the force is zero. If the dipole
is kept finite, the force calcualted, and then the limit taken, the force is
finite.

POINT is compute the forces and then take the averages

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Bob aka RS Eisenberg 
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