_a_ is a circular glass vessel 1 foot 6 inches diameter; _b b_ a tube fixed thereunto; _c c_ are funnels containing valves; _d_, a float of hollow copper, or any light substance; _e_, an open mouth; _f_, an open vessel filled with mercury as high as the dotted line. It is well known that several experiments were made by M. Venturi, Sir Isaac Newton, etc., demonstrating that a vessel shaped thus-- [Illustration] will emit water with a much greater rapidity than a vessel shaped thus-- [Illustration] say, with more than a third as much speed. I propose, then, to have the mouth of the vessel _a_ of the former shape, being the natural form of flowing water. The vessel _a_, and tube _b_, must be completely filled with mercury, by means of the funnels _c c_, which will also contain mercury. In order to set the fluid in motion, the valve in the large vessel _c_ is to be raised; the mercury (which was hitherto held up by a greater weight of atmosphere) will instantly run out of the mouth _e_, and must be suffered to do so till the mercury in _c_ is level with the dotted line; by this time the mercury in _a_ will have obtained a momentum which will be more than equivalent to the pressure of the atmosphere: consequently, the mercury will run out of the large vessel _a_, till it falls as low as the dotted line; the float _d_, resting on the mercury, of course, falls with it, opens the valve, and admits a proportionable quantity of mercury through the tube _b_, driven by the pressure of the atmosphere (the height from the mercury in _f_, to the top of the tube _b_, being only 26 inches, which is 2 inches less than what the atmosphere will at all times raise mercury in a vacuum). [Illustration] By this means will there not be a continual circulation of mercury? Orchard's Vacuum Engine In 1826 there was published in "Mechanics' Magazine," London, a communication from a Mr. Orchard, concerning an invention he considered himself as having made. The account is published in his own words, and is as follows: A is an iron reservoir nearly filled with mercury; B, a tube twenty-four inches long, having its lower end inserted in that reservoir; and C and D, two cocks for the convenience of filling the tube B. From this another tube M proceeds at right angles, to the vessel G. In this latter tube is the cock F, to admit of, or shut off, a communication between the tube and the vessel G. This communication being closed, the tube B is carefully filled with mercury; after which the cock D is closed and the cap E screwed on. [Illustration]