In Dr. Brewster's appendix to Ferguson's lectures, the following description is given of what is called a "Water Blowing Machine": "Let A B (see Fig.) be a cistern of water, with the bottom of which is connected the bended leaden pipe B C H. The lower extremity H, of the pipe is inserted into the top of a cask or vessel, D E, called the condensing vessel, having the pedestal P fitted to its bottom, which is perforated with two openings, M N. When the water which comes from the cistern A is falling through the part, C H of the pipe, it is supplied by the openings or tubes, _m_ _n_ _o_ _p_, with a quantity of air which it carries along with it. This mixture of air and water, issuing from the aperture H, and impinging upon the surface of the stone pedestal P, is driven back and dispersed in various directions. The air being thus separated from the water, ascends into the upper part of the vessel, and rushes through the opening F, whence it is conveyed to the fire, while the water falls to the lower part of the vessel, and runs out by the openings M N." The author then goes on to describe the construction of the pipe B C H, in the curve of which some nicety is required, and to explain some atmospherical phenomena upon the principle of this machine, adding that "Franciscus Tertius de Lanis observes that he has seen a greater wind generated by a blowing machine of this kind than could be produced by bellows ten or twelve feet long." [Illustration] Now, if, instead of the pedestal P, a wheel were placed in the condensing vessel, as in the figure, would not the water, in falling upon the wheel, be sufficiently dispersed to disengage the air at the same time that it drove the wheel, and would not the motion of the wheel be retarded by the density of the internal air?