Treadmill
a wheel driven by the weight of persons treading on the of the periphery; originally an invention of the Chinese to raise water for the irrigation of the fields. It is employed in some prisons, where it forms part of the "hard labor" of persons convicted. The usual form is a wheel 16 feet long and five in diameter, several such wheels being coupled together when necessary for the accommodation of the prisoners. The circumference of each has 24 equidistant steps. Each prisoner works in a separate compartment, and has the benefit of a hand rail. The wheel makes two revolutions per minute, which is equivalent to a vertical ascent of 32 feet. The power may be utilized in grinding grain or turning machinery.
Its use, as part of the machinery of