HYDRAULICS. 199 



If H and H' be the heights of two reservoirs, h and 

 h* the heights of the actual jets, 



H h : H' h' : : 7* 2 : K* . 



This observation was made by MARIOTTE. BOSSUT, n. 

 615. 



The water ascends highest when the jet is not quite 

 perpendicular ; when it is perpendicular, the ascent 

 is obstructed by the water falling back on the as- 

 cending column. 



The height to which the water rises in the jet, is called 

 the height of the effective head. 



The parabola which an oblique jet describes, has its di- 

 rectrix not exactly as determined in 286 ; but at 

 the height of the effective head. 



SECT. II. 



OF CONDUIT PIPES AND OPEN CANALS. 



290. W HEN the water from a reservoir is con- 

 veyed in long horizontal pipes, of the same aper- 

 ture, the discharges made in equal times are near- 

 ly in the inverse ratio of the square roots of the 

 lengths. 



It is supposed that the lengths of the pipes to which 

 this rule is applied are not very unequal. It is an 

 approximation not deduced from principle, but de- 

 rived 



