30 



HYDRAULICS. 



side-pipe c into the upper part b of the 

 cylinder, and would therefore press upon 

 the top of the piston and force it down- 

 wards ; while, at the same time, any air 

 or other fluid that might be contained in 

 the cylinder below the piston could 

 escape through the ascending side-pipe 

 d, and would flow out from the cock at 

 the external orifice f, thus permitting 

 the piston to descend without impedi- 

 ment. Having done so, all that would 

 be necessary to produce its re -elevation 

 would be to turn the lever or handle i of 

 the cock downwards a quarter of a revo- 

 lution, by which the two passages would 

 be put into such a position that the water 

 from e would pass down the side-pipe 

 d, and by entering the lower part of the 

 cylinder would force the piston upwards, 

 the water previously admitted above the 

 piston being by this means expelled at/ 

 through the passage prepared for it, by 

 the above turning of the cock. To stop 

 the machine, the cock is put into an in- 

 termediate position, which shuts all the 

 four orifices at once, or it may be stopped 

 by shutting a cock in the pipe of supply 

 &tg ; and to cause the machine to work 

 of itself without attendance, all that is 

 necessary is to prolong the end of the 

 w r orking-beam k, to which the piston- 

 rod is attached as in the steam-engine, 

 and to fix a plug-tree or rod / 1 to such 

 prolonged beam, when the tappets or 

 projecting pins m m will strike upon 

 and move the lever i of the cock at the 

 proper periods for sending the water al- 

 ternately above and below the piston, 

 and thus keep the machine in constant 

 action. 



This machine is dependant on the prin- 

 ciples of Hydrostatic pressure, and is in 

 every respect similar in operation to the 

 hydrostatic bellows or Bramah's water - 

 press,described in theTreatise on Hydro- 

 statics. In that treatise it is shown that 

 the pressure of fluids is according to the 

 area or surface upon which they press, 

 and the perpendicular height of the co- 

 lumn, without any regard to the quan- 

 tity of water employed, consequently, 

 whatever may be the size of the pipe g 

 which conveys the water, the effect of 

 that water will be as the area of the 

 piston or the cylinder. The pipe g 

 needs therefore be no larger than what is 

 necessary to convey a sufficiently speedy 

 supply into the cylinder a b, for if it was 

 twice or thrice as large, the rapidity of 

 the working alone, and not the power 

 of the machine, would be affected. And 

 since a column of water about thirty- 



three feet high is equivalent to atmos- 

 pheric pressure, or fifteen pounds upon 

 the square inch, so if we suppose the 

 pipe g to be thirty-three feet long from 

 the surface of the water in the reser- 

 voir h, down to the medium point of the 

 cylinder as at e, then that column of 

 water will exert a power to move the 

 piston upwards or downwards equal in 

 force to fifteen pounds multiplied by the 

 number of square inches the piston may 

 contain, without any deduction except 

 what is necessary for the friction of the 

 machine. Now a cylinder only twelve 

 inches diameter, will contain 113 square 

 inches upon its piston, which multiplied 

 by 15 pounds gives no less than 1715 

 pounds pressure upon so small a ma- 

 chine ; and as both the height of column 

 and magnitude of the cylinder may be 

 greatly increased without inconvenience, 

 it will be seen that this is a most excellent 

 and simple machine, affording disposable 

 power applicable to any purpose, when- 

 ever the two requisites for its construc- 

 tion can be obtained, viz., a sufficiently 

 elevated supply to work the piston, and 

 a convenient discharge for the waste 

 water to escape after it has performed 

 its duty. 



So far, the w r eight and moving im- 

 petus of water have alone been noticed 

 as capable of producing power to work 

 machinery ; but a similar effect may also 

 be obtained from the re-action and cen- 

 trifugal force of water in machinery 

 properly constructed for the purpose of 

 obtaining it, and the present account of 

 hydraulic machines shall therefore be 

 concluded by a description of a curious 

 machine invented by Dr. Barker to- 

 wards the close of the seventeenth cen- 

 tury, and which is generally known by the 

 name of Barkers Centrifugal Mill. In 

 this the water does not act by its weight 

 or momentum, but by its centrifugal 

 force and the re-action that is produced 

 by the flowing of the water on the point 

 immediately behind the orifice of dis- 

 charge. Its general construction is 

 shown at fig. 22, in which v u is 

 a metal pipe of considerable height, 

 its top v being widened or extended 

 into a funnel shape. The pipe is 

 maintained in its vertical position, as 

 shown in the figure, by resting on a 

 pointed steel pivot turning into a brass 

 box w at the lower extremity, while the 

 upper part has a cylindrical steel axis 

 passing through the top y y of a frame 

 which supports it : the pipe v u is con- 

 sequently free to move round upon its 



