We have all seen the principle of gyroscopic motion in a child's top, which balances as long as it continues to spin. Any spinning body, such as a wheel or a top, tends to keep its axis of spin always pointed in the same direction. Gyroscopes are not affected by either the downward pull of the Earth's gravity or by the presence of a magnetic field. For those two reasons, a gyroscope can be useful for navigation purposes.

In 1851 the French inventor Jean Foucault built the first gyroscope. It consisted of a rapidly spinning wheel within concentric rings which allowed the wheel to move freely about two axes. It demonstrated the rotation of the Earth because the spinning wheel, which was not fixed, retained its orientation in space while the earth turned under it. Foucault also found that the force of the Earth's rotation caused the gyroscope's axis...