Rhys Kendrick begins with a question that sounds trivial and is not: how do you stop fifty vehicles at once when the person deciding is at the front of them?

The intuitive answer is to send compressed air down the train to push the shoes on, and for a short, sound train it works. The chapter that follows breaks the pipe, and the intuitive answer dies with it. Air escapes at the break, the vehicles beyond it are unreachable, and both halves of a parted train continue with nothing acting on them at all.

What replaces it is an inversion, and the book is built around it. The pipe is kept charged, and that pressure means release. Braking is commanded by taking pressure away, so the worst failure the pipe can suffer becomes identical to the firmest instruction the driver can give. Since the pipe can no longer be the source of the force, every vehicle carries its own reservoir of air, and the train is braked not from the locomotive but by fifty independent machines that happen to agree.

Kendrick devotes several chapters to the triple valve that makes the decision on each wagon: a purely pneumatic device comparing two pressures and choosing among charging, holding and applying, with nothing that could be described as intelligence. He is equally interested in the costs, from the time needed to recharge reservoirs after a release to the wave that carries a pressure change slowly along a very long train, and in the difference that split freight practice from passenger practice.

Electro-pneumatic control, the statute that made the design compulsory, and its peculiar longevity fill the closing chapters. Nine works are cited.