Theory of the Pneumatic Paj^adox. 305 



rie'^ces no effort ; for the velocity of the water having a free and 

 horizontal direction, there can result from it no force which will 

 exert itself against the interior surface of the tube. If proof of 

 this is desired, it is furnished by the following experiment. 



To a large reservoir I adapted a horizontal tube three feet long 

 and nine or ten lines in diameter. Near the middle of it a small 

 lateral hole was made, destined to form a jet which could be di- 

 rected upwards or downwards, or inclined at pleasure, by turning 

 the tube on its axis. The water was kept in the reservoir at the 

 height of about four feet above the tube. When the end N was 

 stopped, the jet had the height such as has been already deter- 

 mined ; but when the end N was unstopped, the jet ceased 

 almost entirely in all directions. Only when the bole M was di- 

 rected downwards, the water dropped a little by its edge. It is 

 evident that the cessation of the jet demonstrates the cessation of 

 pressure against the interior surface of the tube. 



The result thus obtained by Bossut appeared to me so much at 

 variance with what we should expect a priori, when we compare 

 the rapid propagation of pressure in liquids with the very moder- 

 ate velocity of water issuing from an orifice with a head of only 

 four feet, that I was induced to repeat, with various modifications, 

 the foregoing experiment. Having in all of them arrived at simi- 

 lar results, I think I may, without fear of mistake, venture to 

 ascribe that of Bossut to some inaccuracy in his mode of perform- 

 ing the experiment. The grounds of this inference are imme- 

 diately subjoined. 



Experiment I. To the stop-cock of a copper condensing cham- 

 ber having a bore of one eighth of an inch in diameter, was 

 adapted a common brass tube of the same diameter, and about 

 eight inches long, which had three lateral holes at intervals of an 

 inch or two from each other, varying in diameter from an eighth 

 to a twentieth of an inch. Great care was used in making these 

 holes not to leave the slightest protrusion on the inside of the 

 tube, and in no respect to change its form. The condensing 

 chamber having been partly filled with water, and a quantity of, 

 air condensed into it above the water, the stop-cock was opened, 

 and the water being forced through it by the elasticity of the con- 

 densed air, in any position of the tube strong jets of water issued 

 from the lateral holes, reaching, when the tube was in a horizon- 

 tal position and the holes were directed upwards, the height of 

 several feet. 



