44 2 Artificial Fountains, [ Book V 1 1 . 



provided that the ajutage *, and the height of the re- 

 fervoir above the ajutage, is the fame. This is a 

 neceffary confequence of the equal preflure of fluids in 

 all directions. 



Water, when difcharged through an ajutage, however 

 fmall it may be, has a velocity fufficient to raife it to 

 the height of the furface of the water contained in the 

 refervoir ; fo that a vertical jet d'eau throws up the 

 water as high as the refervoir whence it proceeds, if 

 nothing obftructs it. 



There are, however, many caufes which contribute 

 to diminifh the elevation of water by jets d'eau. Firft, 

 the friction in the pipes from the refervoir to the aju- 

 tage ; fecondly, the friction againft the circumference 

 of the aperture ; thirdly, the refiftance of the air to the 

 motion of the column ; fourthly, the gravity of the 

 particles of water themfelves, which, in rifing, lofe fome 

 .of their velocity, and recoil upon thofe which lucceed 

 them. Thus by inclining the pipe a little, we find 

 that the water will rife higher than when it is exactly 

 vertical ; but in this cafe, the effect is not fo agreeable 

 to the eye of the fpectator, as when the water which 

 rifes above the pipe into the air falls perpendicularly, 

 in a manner, back upon itfelf. 



When the ajutage is placed in an oblique direction to 

 the horizon, the force of the projection and the gravity 

 of the water caufe the ftream which afcends into the 

 air to form a parabola, the amplitude of which is in 

 proportion to the height of the refervoir. 



When the ajutage is placed horizontally, the water 

 forms a femi-parabola. 



Fountains elevate the water in proportion as the 

 aperture of their ajutages is large j becaufe, firft, of 



A tube which is fitted to the mquth of the veffel through 

 which the fountain is played. 



2, two 



