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The horizontal machine driven by muscle-power was not only much more efficient than the vertical machine, but came in a greater variety of forms. It was more efficient because effort could be applied with a greater movement or was more useful since it could incorporate gearing that increased speed or accepted a greater load. Of the various principal types of horizontal machine, the first was the one in which the animal was coupled directly to the moving parts: the apple-crusher in a cider mill is the best-known example in Britain. Here a heavy stone roller was rotated by an animal pulling it around a circular trough in which the apples to be pulped were placed. The second type used the animal to turn a drum mounted on a central shaft to wind up a rope and so bring water out of a deep well or minerals out of a mine. The third type was the one that had the greatest application for our agricultural and industrial growth: here the machine was geared to create a mechanical advantage in the use of animal-power. These geared machines fell into two types: the first was that whereby the animal was harnessed to a shaft so that it passed round outside the machine but had to step over the drive shaft between it and the machinery it was powering; the second was that whereby the animal was harnessed under a large diameter gear wheel and the drive to the other machinery was carried at high level. There were, of course, variants on these such as the paddle wheel and the oblique tread wheel. In the case of the paddle wheel the animal stood harnessed on an inclined plane which was in effect a belt which moved under the animal, thereby transmitting power by means of gears or belting to the machinery. The oblique tread wheel was a circular tread plate on which the animal was tethered. The plate was then mounted with its shaft at an angle to the vertical, and, as the circular tread plate moved away from under the animal, a gear on the underside of the plate transmitted power to the machinery by means of the shaft.
Which one is not discussed in the passage?