Mark Carney, the newly appointed governor of the Bank of England, will be paid about £1 million a year, all in. That cannot be the right amount. It is either way too much or way too little.

To see why, begin by supposing that monetary economics is an advanced science, that economists have discovered the relationships between interest rates, the money supply, inflation and other relevant economic variables. This would make Mr. Carney's job dead easy. He need only get some diligent secondary-school children to plug the relevant...