The Old Pole Burner is entirely correct about all of this. Actually, the skin effect of alternating current flowing on the outside of transmission wires can be taken advantage of. When very long aerial apans of transmission wire are made, high-tensile-strength steel wire is used because its strength is needed to hold up its own weight. The steel wire is then clad with aluminum. Since the alulminum is on the outside, the skin effect of the current flowing on the outside of the wire benefits from the low resistance of the aluminum. Very little current flows through the inner steel wire.