Treadmill
2 of the 7 encyclopedias on this shelf carry an entry for Treadmill. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
a contrivance for driving machinery by utilizing the weight of persons or of domestic animals. An endless apron is mounted on rollers. One end rests near the ground, the other is somewhat elevated. Slats are fastened across the apron to form steps. In the case of domestic animals, the apron is inclosed usually in a frame like a stall. As the animals tread the apron, it turns away beneath them, causing them to climb continuously. A pair of horses, for instance, tied in the stall, climb away hour after hour, turning the apron. One of the rollers around which the apron is fastened turns a wheel, from which a belt passes to the machinery which it is desired to operate. This is a favorite method of operating portable wood saws. Formerly a dog was used to operate the dasher of a churn. The threshing machine in vogue during the first half of the nineteenth century was operated by a treadmill. A modification of the treadmill has been used from time to time as a punishment for criminals. A person fastened by the arms in a stall of this sort is obliged to tramp incessantly to prevent himself from falling forward in a painful way upon his face. "Turning a treadmill" is a proverbial expression for monotonous drudgery. Thus we speak of the treadmill of life, the treadmill of industry, etc.
Collier's New Encyclopedia (1921)
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 restricted, as the weak and strong are by it compelled to equal exertion.