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 four field equations, for the case of a moving point charger,-

where R is the radius vector connecting the moving charge with the point in question and $$\psi$$ is the angle between R and v.

For the field acting on the test electron $$t$$, situated at the point $$x=0$$, $$y=y$$, we may substitute $$\mathsf{R}=y\mathsf{j}$$ and $$\sin\psi=1$$, giving us,

and

substituting into the fifth fundamental equation of electromagnetic theory,

we obtain the force acting on the unit test electron $$t$$.

[Note in the above equation that v, the velocity of the electron, is for our case $$v\mathsf{i}+u_{y}\mathsf{j}$$.]

or

Under the action of the component force $$\mathsf{F}_{x}$$ we might at first sight expect the electron $$t$$ to aquire an acceleration in the X direction: Such condition, however, would not be in agreement with the principle of relativity, since from the