Consider a transition from ,
Consider another transition from , (This is an extrapolation, it is not proven that is a solution.)
such that, is in between the paths of and .
If we take the geometric mean of the two,
and let
Jm-1
We have an expression for . A negative sign is necessary because a change from a higher value of to a lower value of (ie. a positive value of ) results in a loss of energy.
Note: If,
And,
And,
--- (*)
This does not proof that is a solution to for but it shows that (*) is a valid expression.