Dale, The solution to the puzzle I mentioned earlier lies in the fact that, in the third link, the magnetic force was calculated to order v^2 but the electric force was not. This is inconsistent. If you look back at my post, you will see that the transverse (to the motion) electric field picks up a factor of γ so the electric force is not simply e^2 / 4 D^2 i but rather γ e^2 / 4 D^2 i . This force is clearly corrected from the v = 0 result by a term of order v^2. To be precise, γ e^2 / 4 D^2 i ~ (1 + 1/2 v^2) e^2 / 4 D^2 i . The magnetic force is - v^2 γ e^2 / 4 D^2 i (factor of γ here too!), but to order v^2 we can simply ignore the γ. The result when you add everything together is (1 + 1/2 v^2 - v^2) e^2 / 4 D^2 i = (1 - 1/2 v^2) e^2 / 4 D^2 i , thus resolving the problem. Note that the ratio of the two forces as calcaluted in the third link is indeed correct for small v, and actually it holds for arbitrary v as you can see above.