FORM OF JETS 123 



2 



where C = coefficient of discharge. 



Where the upper surface remains at the same level we have the state 

 of affairs which holds during the filling of a canal lock through a sub- 

 merged orifice in the lock gate. The upper surface is in effect now of 

 infinite area, so that putting AI = oo in equation (1), we get the time of 

 filling the lock. 



n / n ^ x jr 



C a v 2 r/ 



With submerged orifices the value of (7 is about '61, diminishing slightly 

 with an increase in the effective head HI H 2 . 



ART. 47. FORM OF JET. 



m 



Where a jet issues from an orifice in the horizontal base of a vessel, 



its sectional area gradually diminishes as the velocity increases, until it 



I finally breaks up into a series of detached drops. With a circular orifice 



I this is the most noticeable feature. With any other form of orifice, 



however, the jet after escaping suffers a continuous change in the form 



jof its cross section. This is due to the effect of the tension of its surface 



'film, which tends in the first place to bring the jet into the circular 



orm. The inertia of the particles of water causes this effect to be 



lightly overdone, so that a continual alteration and realteration of 



ection takes place, the jet finally if sufficiently large in diameter and of 



ufficient height settling down into a circular section. The action is 



>eriodic and approximately isochronous, and consequently with a steady 



et the section at any fixed point is constant. 



Where a jet escapes from an orifice in the vertical side of a vessel 

 i second disturbing factor now affects its form, for since the velocities 

 f efflux at points on a vertical diameter of the orifice increase with the 

 lepth, the trajectories of any two particles situated in the same vertical 

 lane will intersect if produced. 



This has the effect of narrowing the jet in the direction of its depth, 

 ind, by the consequent impact of particles, causing it to become wider in 

 i horizontal direction. Surface tension prevents dispersion of the stream, 

 ind brings the diverging particles back towards the axis of the jet and in 

 i horizontal plane. The consequent impact causes the jet to become 

 larrower in a horizontal direction and increases its depth, and a continual 



