THE WORK OF AIR AND WATER 



an indefinite power to move weights through a short 

 distance, with the expenditure of very little working 

 energy. The principle on which the hydrostatic press 

 is based is the one which was familiar to the ancient 

 philosophers under the name of the hydrostatic para- 

 dox. It was observed that if a tube is connected with 

 a closed receptacle, such as a strong cask, and cask 

 and tube are filled with water, the cask will presently 

 be burst by the pressure of the water, provided the 

 tube is raised to a height, even though the actual weight 

 of water in the tube be comparatively slight. A power- 

 ful cask, for example, may be burst by the water poured 

 into a slender pipe. The result seems indeed paradox- 

 ical, and for a long time no explanation of it was forth- 

 coming. It remained for Servinus, whose horseless 

 wagon is elsewhere noticed, to discover that the water 

 at any given level presses equally in all directions, and 

 that its pressure is proportionate to its depth, quite 

 regardless of its bulk. Then, supposing the tube in 

 our experiment to have a cross-section of one square 

 inch, a pressure equal to that in the tube would be 

 transmitted to each square inch of the surface of the 

 cask; and the pressure might thus become enormous. 

 If, instead of a tube lifted to a height, the same tube 

 is connected with a force pump operated with a lever 

 an apparatus similar to the fire-engine of Ctesibius it 

 is obvious that precisely the same effect may be pro- 

 duced; whatever pressure is developed in the piston 

 of the force pump, similar pressure will be transferred 

 to a corresponding area in the surface of the cask or 

 receptacle with which the force pump connects. In 



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