Electric charge consists, therefore, in an excess or deficit of negative electrons in a body.
A collision may be able to throw the electrons from one of these positions to another.
Rutherford had announced the nuclear theory of atomic structure which required each atom to consist of a minute positively charged nucleus about which negative electrons were distributed.
True electric current arises solely from convection of the atomic charges or electrons; this current is therefore not restricted as to form in any way.
For purposes of theoretical discussions relating to moving radiators and reflectors, it is important to remember that the dynamics of all this theory of electrons involves the neglect of terms of the order (v/c) 2, not merely in the value of K but throughout.