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A car with just two wheels looked too terrifying to catch on, but the secret of its amazing balancing act is at the heart of today’s guidance systems

LOUIS BRENNAN was an Irish-Australian engineer who devised a deeply unlikely form of transport: the gyro car whose two wheels were one in front of the other, like a bicycle (see photo, below). It proved to be a dead end, but it blazed a trail for a transport revolution.

Gyroscopes exploit the principle that a rotating object tends to conserve its angular momentum: once it starts spinning, the wheel of a gyroscope resists any force that tries to change its spin axis. Brennan realised that a gyroscope could keep a monorail upright and in 1903 patented the idea. He demonstrated a scaled-down prototype monorail at a in London in 1907 and “aroused the amazed interest of the world” . The celebrated author H. G. Wells alluded to the event in his 1908 novel, The War in the Air, and described how the audience was concerned by the idea of a gyro car crossing an abyss on a wire cable: “Suppose the gyroscope stopped!”

Brennan went on to demonstrate a full-scale version in 1909 but, as Wells had suggested, safety fears discouraged its commercialisation. Here, Elmer Sperry enters the story. Having been working on his own gyroscope technology, he bought Brennan’s patents and went on to found the Sperry Gyroscope Company in Brooklyn, New York, to pursue marine applications including gyrocompasses and ship stabilisers. Today, devices developed by Sperry and others are ubiquitous. Gyrocompasses use the gyroscopic principle to keep the needle pointing north, and gyroscopes are also at the heart of related guidance, steering and stabilisation equipment on warships, oil tankers, missiles and more.

“Gyroscopes are crucial in the systems used to steer, guide and stabilise today’s ships”

Some see a parallel between the unfounded fears that made Brennan’s gyro-stabilised vehicles look unlikely and current opposition to some modern technologies. Brennan’s monorail worked on sound principles but people feared that malfunction might cause disaster. Sperry used the same scientific principles but concealed them in the technology so they were not perceived as being risky, according to David Rooney of the Science Museum in London. “Many people still voice Wells’s metaphorical concerns,” he says. “What if the scientists get it wrong? Are we heading for a fall?”

Read more: Zeros to heroes: 10 unlikely ideas that changed the world