Asimov wrote:

I think a saturable core can be used to measure a static magnetic
field. Early computer magnetic core memories worked like this.

I was referring to the similarity to a rotating coil gaussmeter. I
think what you're describing now is something more akin to the fluxgate
magnetometer.

Relativity transforms static fields into dynamic fields by adding a
velocity component to the measurement.

I see. Is Omni magazine still in print by any chance?

That Leyden Jar experiment was measuring charges not the E field
itself.

Leyden jars store charge. As I said before, they produce an indication
by relying on the electric field between charged surfaces and the
resulting Coulomb force. The more charge stored in the jar, the greater
the electric field. Charge, E field, and Coulomb force all being in
proportion, the Leyden jar produces a response in proportion to all three.

jk