In this article work begun in a previous one, Reference 20, is continued. Two matters especially are considered. One is the increase of mass of charged elementary particles moving at high speeds. Special relativity includes this increase, but offers no physical explanation; it is hard to see how arguments about observers can explain what happens when no observers are present. Here the increase of inertia is seen to be due to the magnetic field generated by the motion. The other matter is the stability of elementary particles such as electrons. These particles are basic to electrodynamics; but electrodynamics, predicts, that the particles would explode, unless there be additional forces to bind them together. Here such a binding force is investigated and an incidental outcome of the investigation is the removal of a discrepant factor such as 4/3, which has long plagued theories of the electron.