Theory of the Pneumatic Parador. 305 
riences 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 hole 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. 
