DISCHARGE OF WATER THROUGH ORIFICES AND PIPES. 191 



Fig. 158. ^ ^|-^g stream will be considerably con- 

 tracted {Fig. 158). If a short tube be 

 inserted into the hole (the head being 

 the same), this crossing of particles will 

 be partly prevented, and the liquid will 

 flow more rapidly. The greatest ef- 

 fect is produced Fi?. iso. Fig. leo. 

 when the tube 

 is twice as long 

 as its diameter 

 (F«V. 159). If 

 the tube be en- 

 larged at its 

 , ,,» upper and low- 

 'I'lll'l er end, similar 

 to the form of the contracted 

 stream of water in Fig. 158, the quantity 

 discharged is greatly increased {Fig. 160). 



When water flows down an inclined plane, the same 

 law applies as to the motion of a sohd body rolling down 

 a plane. The velocity increases as the square of the dis- 

 tance, and is the same as the velocity of a body falling 

 freely downward from a height equal to the perpendic- 

 ular height of the plane. Unless the stream, however, is 

 very large, its speed is quickly diminished by the friction 

 of its chamiel,* until this friction becomes as great as 

 the descending force, after which the motion becomes 

 uniform. Hence the reason that large streams, with an 

 equal degree of descent, flow so much more rapidly than 

 small ones, the gravitating force being so much great- 

 er that friction has a less retarding effect upon them. 



* Which increases as the square of the velocity. 



