**Abstract**

In this book chapter the electromagnetic force between two parallel electric conduc‐ tors has been derived, applying thereby the effects of propagation delay and the Spe‐ cial Relativity theory, taking thereby also into count the thus far neglected effects introduced by the voltage sources of both circuits. This has been done for a specific case consisting of two rectangular circuits, aligned to each other along one of the long sides, at a distance that is short compared to the long sides. The intention in doing so is to make a meaningful application of the concept of "two parallel conductors of in‐ finite length", so that it is possible to make a complete calculation of the force between the two circuits, avoiding thus making a vague claim as for example Maxwell, saying that the other parts of the conductors do not contribute to the force. What is radically new in this interpretation is that it is Coulomb's law that is responsible for the force.

**Keywords:** Ampère's Bridge, Ampère's Law, Coulomb's Law, electromagnetic force, Lorentz force, Lorentz transformation, parallel conductors, propagation delay, retard‐ ed action, Special Relativity theory, Sagnac effect, time dilatation
