265 
by signs the action of machinery. 
quantity of air at each stroke ; it opens when the valve C is 
just closed, and a regurgitation takes place in the supplying 
pipe just previous to the opening of the great valve. Without 
this contrivance, the pressure on the air in the air vessel 
would cause it to be soon absorbed by the water, and the 
engine would cease to act. 
In this notation two indicating lines A, A, are allowed to 
the supplying water, because it takes three different courses 
during the action of the machine. The first of these marks 
the time of its motion when it enters the air vessel, and the 
second indicates its course when passing through the great 
valve, and also its course when, owing to the elasticity of the 
materials, its motion is for an instant reversed, at which 
moment air is taken in at the air valve F. 
The action of the machine is as follows : the supplying 
water rushing along the great pipe passes out at the great 
valve ; it acquires velocity until the pressure of the effluent 
water against the under part of the great valve causes it to 
close suddenly. At this moment the whole momentum of 
the water is directed against the sides of the machine, and 
the air valve being the weakest part gives way, and admits 
a small quantity of water ; the air spring soon resists suf- 
ficiently to close the air valve : at this moment the elasticity 
of the apparatus re-acting on the water in the great pipe, 
drives it back for an instant, during which the pressure of 
the atmosphere opens the air valve, and a small quantity of 
air enters ; this finds its way to the air chambers, which 
easily discharges it through the ascending pipe if too much 
air has entered. 
