In today Physics, Electromagnetism requires a constant speed-of-light. Indeed, Gravity needs a variable speed-of-light.
How can we solve it? The answer is that physical dimensions of bodies, as well as the electric charge, vary "according to the speed-of-light".

1. Capacitance, Inductance and Resistance (P. Galletti and A. Aluigi)
Rome, 31 January 2004

Bodies "plunged" into a Gravitational Field varies their dimensions "according to the speed-of-light". The dielectric constant as well as magnetic permeability increase with the density of "space", but Capacitance, Inductance and Resistance of electrical circuits keep still constant.

As a consequence, an LC (or RC) oscillator (clock) does not vary in a Gravitational Field.

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