HYDKAULICS. 



149 



Upon what docs 



What is the ve- 

 locity of a liq- 

 uid flowinsfrom 

 a reservoir 

 equal to ? 



335. When an opening is made in a rescr- 

 flowTng^ifqum "^^i'' containing a liquid, it will jet out with a 

 depend? velocitv x^r^poi'tiuncd to the depth of thcai^cr- 

 ture below the surface. 



Fig. 140 Supposing the stirface of water in a vessel, D, Fig. 



140, to be kept at a constant height by the water 

 flowing into it, and that the water flows out through 

 oppningg in the side of precisely the same size ; then 

 a quart measure would be filled from the jet issuing from 

 B as soon as a pint measure from the upper opening, A. 

 As the flow of liquids is in consequence of the at- 

 traction of gravity, and as the pressure of a liquid in 

 /*; equal in all directions, we have the following princi- 

 ple estabhshed: — 



336. The velocity which the particles of a 

 liquid acquire when issuing from an orifice, 

 whether sideways, upward, or downward, is 

 equal to that which they would have acquired 



in falling perpendicularly through a space equal to the 

 depth of the aperture below the surface of the liquid. 



Thus, if an aperture be made in the bottom, or side, of a vessel containing 

 water, 16 feet below the surface, the velocity with which the water will jet 

 out will be 32 feet per second, for this is the velocity which a body acquires 

 in falling through a space of 16 feet. 



As the velocity acquired by a falling body is as the square root of the space 

 through which it f;ills, the velocitj' with which water will issue from an aper- 

 ture may be calculated by the following rule : — 



337. The velocity with which water spouts 

 out from any aperture in a vessel is as the 

 square root of the depth of the aperture below 

 the surface of the water. 



The water must, therefore, flow with ten times greater velocity from an 

 opening 100 inches below the level of the liquid, than from a dejjth of only 

 one inch below the same level. 



338. The theoretical law for determining the quantity of 

 water discharged from an orifice is as follows : — 



The quantity of water discharged from an ori- 

 fice in each second may be calculated by multi- 

 plying the velocity by the area of the aperture. 



The above rules for calculating the velocity and quanthy of water flowing 

 from orifices, are not found strictly to hold good in practice. The friction 

 of water against the sides of vessels, pipes, and apertures, and the formation 



How may the 

 velocity of a 

 liquid flowing 

 fiom a reser- 

 voir be calcu- 

 lated ? 



What is the 



f!ieorpticall:iw 

 for determin- 

 ing the qnan- 

 tit of water 

 discharged 

 from an aper- 

 ture ? 



