In which Frank discovers that his conveyances are too heavy for contemporary bridges.

This is actually the end of the story, and a rare example of using the inevitable destruction of the vessel as high-point worthy of cover status.

What a pity! This vehicle was quite different:

Frank was proud of this machine.
He had discovered that magnetism could be made as useful for power as electricity was for motive force.

He abandoned magnetism for subsequent inventions, it seems. It's not as much fun as electricity. Magnetism is quiet and invisible. Electricity is sparkly and crackly and has bolts!