There is a catch though: You can never get a pure magnetic field by reference frame change from a pure electric field, and vice versa, for

$$F_{\mu\nu} F^{\mu\nu} = \ 2 \left( B^2 - \frac{E^2}{c^2} \right) = \mathrm{invariant}.$$

In other words, starting with a pure electric field, you can only obtain a mixed electric and magnetic field, but never a pure magnetic field.

In this sense, magnetism is not just another form of electricity, though they are closed related.

There is a catch though: You can never get a pure magnetic field by reference frame change from a pure electric field, and vice versa, for

$$F_{\mu\nu} F^{\mu\nu} = \ 2 \left( B^2 - \frac{E^2}{c^2} \right) = \mathrm{invariant}.$$

In other words, starting with a pure electric field, you can only obtain a mixed electric and magnetic field, but never a pure magnetic field.

In this sense, magnetism is not just another form of electricity, though they are closely related.