H YDR OKINETICS. 



149 



The ordinary river current is from three to five miles per 

 hour. 



259. The Flow of 

 Liquids through Verti- 

 cal Pipes. Liquids flow ing 

 freely through vertical pipes 

 exert no lateral pressure. 

 The liquid will not wholly 

 fill the tube, but will be sur- 

 rounded by a thin film of air. 

 These air particles will be 

 dragged down by the adhe- 

 sion of the falling liquid. 

 If a small tube t be inserted 

 near the top of the vertical 

 pipe a current of air will be 

 forced through it and down 

 the pipe. This air current 

 may be utilized for blow- 

 pipe and other purposes. 

 With a long discharge pipe, 



the force with which the air is drawn through t 

 may be used to remove the air from a vessel, R. The 

 apparatus then becomes a Sprengel's or Bunsen's 

 air-pump. ( 290, 291.) 



260. Water-power. Water may be used to turn a 

 wheel and thus move machinery by its weight, the force of 

 the current, or both. The wheels thus turned are of 

 different kinds; the availability of any one being deter- 

 mined by the nature of the water supply and the work to 

 be done. 



FIG. 87. 



