18 



GENERAL FORMATION, &c, OF GARDENS. 



instance, will be found the cheapest in the 

 end, as, when once put into operation, it 

 is scarcely possible for them to get out of 

 working order ; and hence all the expense 

 of pumping, and the necessary repairs 

 attending it, are dispensed with. Various 

 hydraulic powers might be employed for 

 this purpose : the simplest and best is the 



Fig. 



belier hydraulique, or water-ram. We say 

 the best, because it is effective, and of such 

 simple construction as to be scarcely ever 

 out of order, and, when once set in motion, 

 it goes on incessantly without any external 

 aid, so long as it is supplied with water. 



Fig. 9 represents this machine, and the 

 following description explains its action : 



0 









1 r 





1 1 













i 



1 1 1 1 



" Suppose o to represent a cistern or 

 reservoir, or the source of a spring which 

 is constantly overflowing or running to 

 waste, by means of a channel a few feet 

 lower than itself, as at the level line pp. 

 Instead of permitting the water to run 

 over the sides of o, let it be conducted to 

 the level pp by means of iron or other 

 pipes, q q, connected with the side of the 

 reservoir, and terminating by an orifice, 

 r, in which a conical or other valve, s, is 

 placed, so as to be capable of effectually 

 closing the pipe when such valve is drawn 

 upwards : t is an adjustable weight fixed 

 on to the spindle of the valve s, by means 

 of which the valve is kept down and open ; 

 any water, therefore, that is in the cistern 

 o, will flow down the pipe q q, and escape 

 at the orifice r, so long as the valve re- 

 mains down ; but the instant it is raised 

 and shut, all motion of the water is sus- 

 pended. Thus situated, the adjustment 

 of the weight t must take place ; and by 

 adding to, or subtracting from it, it must 

 be made just so heavy as to be capable of 

 sinking or forcing its way downwards 

 against the upper pressure of the water, 

 the force of which will depend upon the 

 perpendicular distance from the surface 

 of the water in o to its point of discharge 

 at r, represented by the dotted line o v. 

 But the water, by moving, acquires a mo- 

 mentum and new force, and consequently 

 is no longer equal to the column o v, to 



which the valve has been adjusted, but is 

 superior to it, by which it is enabled to 

 overpower the resistance of the weight t, 

 and it carries the valve up with it, and 

 closes the orifice r. This is no sooner 

 done than the water is constrained to 

 become stationary again, by which the 

 momentum is lost, and the valve and 

 weight once more become superior, and 

 full, thus reopening the orifice and per- 

 mitting the water to move again ; and as 

 the pressure of the water and the weight 

 of the valve each become alternately su- 

 perior, the valve is kept in a, constant 

 state of vibration, or of opening and 

 shutting, without any external aid what- 

 ever. Such is the principle upon which 

 the motion of the water in the pipe q q is 

 produced ; but the momentum generated 

 cannot be instantly annihilated, and it is 

 not only of sufficient power to raise the 

 valve s, but likewise to burst open the 

 lower end of the pipe q q, unless a suffi- 

 cient vent be provided by which this ac- 

 cumulated force can escape : accordingly, 

 a second valve, u, is placed near the lower 

 end of the pipe q q, and is made to open 

 upwards into the air-vessel, having a dis- 

 charging pipe x'y and consequently, when- 

 ever the valve s is closed, the water, which 

 otherwise would have flowed from the 

 orifice x, now opens the valve u, and enters 

 the air-vessel, until the spring of the 

 contained air overcomes the gradually 



