Measures to secure a patent for the above have been taken by John Smith, of Parmelia, N. Y. The apparatus which forms the subject of this invention differs from the ordinary tide mills, in being altogether independent of any return or current. It may be employed in any tidal water, and is particularly well adapted for use in harbors and docks, for the purpose of driving hoisting machinery for loading and unloading ships. It consists of a vessel or float of adequate buoyancy, which is confined by any suitable means so that it can only move vertically. It carries a vertical toothed rack gearing with a pinion, so placed as to be capable of giving motion to the machinery, which the power is to drive, or is furnished with other suitable means of transmitting the same as it rises and falls with the tide. In order to obtain the same amount of power at the above different changes, it is necessary that the weight of the float should be sufficient to produce the required power, and that it should be sufficiently buoyant to bear at least an equal amount of additional weight, these two desiderata being regulated by the admission of a certain quantity of water to the interior of the vessel.