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Then the gyrostat, mounted with its axis vertical on trunnions on a level with the fly-wheel, and resting on a wooden frame carried about by the professor!

A gyrostat consists of a disk or wheel with a massive rim, which revolves within a case or framework, by which the whole arrangement can be moved about, or supported, without interfering with the wheel.

Figure 15 shows one form of gyrostat mounted on a horizontal frame, held in the hands of an experimenter.

If the fly-wheel be not in rotation, the experimenter can carry the arrangement about, and the fly-wheel and case move with it as if the gyrostat were merely216 an ordinary rigid body.

But now remove the gyrostat from the frame, and set the wheel in rotation.