You're correct in pointing out that Galilean transformation are not 100% accurate for electromagnetism - classical mechanics doesn't apply at the speed of light. Lorenz transformations between inertial frames show that Maxwell's equations (as opposed to simplifications like Coloumb's law or Bio-Savart's law) hold for any frame of reference, whether at slow speeds or close to speed of light. Thus an analysis based on Maxwell's equation applies to any inertial reference frame - there is no preferred one.

Thompson was measuring: e charge / mass of electron Millikan was measuring: e charge

Both measuring e/m and m and e. Final point put Einstein.

@@yuryrabyshko4837 ok

@@yuryrabyshko4837 ok, thanks, and this was my reply to your other comment: You're correct in pointing out that Galilean transformation are not 100% accurate for electromagnetism - classical mechanics doesn't apply at the speed of light. Lorenz transformations between inertial frames show that Maxwell's equations (as opposed to simplifications like Coloumb's law or Bio-Savart's law) hold for any frame of reference, whether at slow speeds or close to speed of light. Thus an analysis based on Maxwell's equation applies to any inertial reference frame - there is no preferred one.

​@@danielfromca1. В природе не существует инерциальных систем отсчета. 2. Уравнения Максвелла инвариантны относительно преобразований Галилея в полных производных. Но! Преобразования Максвелла инвариантны относительно преобразований Лоренца в частных производных.