chap. xx. j FLOW OF LIQUIDS THROUGH TUBES. 211 



the surface of the water in the bottle. The pressure 

 outwards at b is, accordingly, the atmospheric pres- 

 sure the pressure of a liquid column from a to the 

 surface -f the pressure of a liquid column from b to 

 the surface. The liquid column from b to the 

 surface is made up of the column from a to the sur- 

 face, and the column from b to a. The and -j- of 

 the column from a to the surface, therefore, eliminate 

 this factor, and the result is that the pressure at 

 b is the atmospheric pressure + that of the liquid 

 column between 6 and a. This is constant so long 

 as the level of the fluid is above a, and, therefore, 

 for a considerable time the outflow is of constant 

 quantity. This arrangement of Marriotte's will be 

 found adapted to the frog-heart apparatus described 

 on page 236. 



Flow of liquids through imiform tubes. 

 The law of Torricelli is not applicable to the flow of 

 fluids through tubes. Into this, elements of friction 

 and resistance enter 1 2 , 



which alter the results. 



Let A (Fig. 102) be 

 a reservoir filled with 

 water, and let the hori- 

 zontal tube ab be in 

 communication with it 

 an opening o 



the lower part of 

 one side, the velocity 



of efflux at the end b does not obey Torricelli's 

 law. The reason is apparent. The water in its 

 course through the horizontal tube experiences re- 

 sistance by its friction against the walls. The fluid 

 tends to adhere to the walls of the tube, the mole- 

 cules of the fluid, that is, that are in immediate con- 

 tact with the walls. Their rate of flow is thereby re- 

 tarded, and the molecules streaming along the centre 



through 

 at 



