produced by a Fluid in Motion. 105 



to a flow of 300 cub. centims. per minute, water passed from 

 the descending stream through B to the tube A, and quickly- 

 restored the level which the more rapid current had rendered 

 unequal. 



At the commencement of the experiment the particles of water 

 in B are at rest ; as soon as water flows from D, the par- 

 ticles exposed at C pass into the descending stream, and par- 

 ticles immediately behind these rush forward to fill the vacated 

 places; but the greater the number of particles removed, the 

 greater is the force tending to draw them back into A ; for the 

 pressures become more and more unequal, and more and more 

 force is stored up in each of the particles of water in B above 

 the water-level in A. Thus there is a strain upon the particles 

 which acts against the lateral force of the stream from D, and 

 the amount of water removed from A gradually becomes less, 

 until a point is reached at which the pressure of the column of 

 water in the longer limb of B exactly balances the force exercised 

 by the descending stream; water then ceases to be removed 

 from A. 



In the last experiment, as long as the water flowed with a 

 certain velocity, the weight of the column of water in B, tend- 

 ing to equalize the levels, was incompetent to draw water from 

 the current, because it would have to stop a certain amount of 

 motion before it could do so ; but when the velocity of the cur- 

 rent was diminished, the weight of the column of water in B 

 became competent to stop the motion of the particles of water, 

 and therefore to equalize the pressures by drawing water from 

 the descending stream. 



/3. Steam-jet. — The first experiments with a jet of steam were 

 made to determine the variation produced in the lateral-action 

 effect by changing the angle at which the jet impinged upon 

 the orifice of a discharge tube; and the effect was measured in 

 the same manner as that employed to measure the lateral effect 

 of a jet of water. The steam was allowed to attain a pressure of 

 304 millims. of mercury*, and to escape through an orifice 4*5 

 millims. diameter placed 6 millims. from the orifice C of the tube 

 B (fig. 4) ; the same tubes were used, and the experiments were 

 conducted in the same way as with the water-jet experiments 

 described above. The rush of steam lasted about ten seconds 

 at the above pressure, during which time the various amounts 

 of water given below were removed from the tube A (fig. 4) . 

 The tube B was first filled with water, and afterwards left empty ; 

 so that in the one case the steam impinged against a surface of 

 water, and in the other against a surface of air. In fig. 5 the 



* Equal to "4217 kilogramme on a square centimetre, or to 6 lb. on a 



square inch. 



