64 ANNUAL OF SCIENTIFIC DISCOVERY. 



increasing gradually in -width, until its edge intersects the inner sur- 

 face of the opening in the suction side of the piston ; from which line 

 to its extremity at the boss its edges are parallel to each other, and at 

 right angles to the axis of the shaft. An annular opening is left all 

 round the circumference of the discs, the area of which is equal to that 

 of the opening for the admission of water to the piston through a cir- 

 cular aperture in one of its sides. The piston is enclosed in a case of 

 circular form, in one side of which is a circular opening, through which 

 passes the suction-pipe, its end tightly secured by a collar to a corre- 

 sponding projection in the side of the piston. The discharge-pipe is 

 placed vertically on one side of the receiver ; and in an opening oppo- 

 site the suction-pipe is fixed a hollow nut to equalize the lateral pres- 

 sure on the piston. The main journal of the shaft is attached to the 

 hollow balancing-nut, passing through a proper stuffing-box and gland, 

 to render the whole properly water-tight. In cases of fire, a pump on 

 Mr. Gwynne's plan, Avith a discharge-pipe of nine inches diameter, will 

 throw 4000 gallons per minute ; and with a piston of 48 inches diam- 

 eter, (the pump making 400 revolutions per minute,) the water would 

 be raised from mines to a height of 120 feet. 



SYPHON FILTER. 



THE Syphon Filter is, perhaps, the most convenient kind for general 

 purposes, as it may be readily carried about and used by any ordina- 

 rily available pressure. The shape of the filter is that of an elongated 

 bell. It is made of white metal ; and, at the top of the well-shaped 

 vase, there is inserted an inflexible metal tube, furnished with a stop- 

 cock near the end. The vase is filled with powdered quartz, of 

 various degrees of fineness, and the mouth of it is closed with a per- 

 forated cover. When required to be used, the vase is inverted in the 

 water to be filtered, and the tube is allowed to hang below it. When 

 the air is withdrawn, the water rises through the powdered quartz, 

 and fills the tube ; and, by syphonic action, the water is drawn down 

 by its superior gravity. The lower the tube the greater the pressure, 

 for the weight of water flowing down operates on the filtering surface 

 as directly as if the same column of fluid were placed above it. The 

 amount of pressure is, however, limited to that of the pressure of the 

 atmosphere ; for were the tube lengthened beyond 30 feet, the column 

 of water would separate and leave a vacuum. This filter renders the 

 muddiest water beautifully clear when acting with the pressure of not 

 more than two feet at the rate of four gallons an hour. Report on the 

 Great Exhibition. 



PNEUMATIC PILE FOUNDATION. 



THE Civil Engineor and Architect's Journal, for December, fur- 

 nishes the following description of a system of foundation extensively 

 used in Great Britain, but little known or appreciated in this country. 

 The method in question is known under the name of Potts' Pneumatic 

 Process, and consists in em ploy ing as piles, hollo w iron cylinders, to the 



