Mr Dickson on a ne^ Water-Pressure Engine, IW 
pose, the pipe M continued, (at any slope), and the end of it im-^ 
mersed in water, the surface of which is 34 or more feet perpen^ 
dicular below H, then, whenever the valve G or H is opened^ 
the water issues into a vacuum, and is therefore totally freed from 
the resistance of the atmosphere ; therefore the power of the en- 
gine must be increased, in the same manner as if a column equal 
to the weight of the atmosphere were added to the column A. 
That no water may pass along without entering the cylinder, 
one set of valves shuts before the other set opens ; and as water 
is nearly incompressible, every time it is stopped, or its course 
suddenly altered, when confined, as in this machine, it would 
give a shock to its several parts, and tend to loosen its joints. 
To counteract these effects in the upper column, the air-vessel 
O is placed on the pipe that leads to the cylinder, as near it as 
convenient ; and when any set of valves is shut, the water in A 
rushes into O, and condenses the air in it more than the weight 
of the column A at rest would do. Hence, when the next set 
opens, the water is pressed out, and a current is also continuing 
to descend along A. The air-vessel P, which is joined to the pipe 
leading from the cylinder, gives to that pipe a more equal cur- 
rent than it would have without it ; for when one set of valves 
is shut, the column in M would be suspended till the other set 
opens, which would give a concussion to the whole machine. 
Before the machine, therefore, is put in motion, the stop-cock 3 
is shut, and 1 and 2 opened, and the water running into P ex- 
pels the air through a small cock, the end of which goes down 
into the top of the vessel about an inch. Let us now suppose 
one set of valves shut, then' a current will begin to flow out of P, 
and the air that was not allowed to get out of the top of the vessel, 
will be dilated ; consequently, when the other set of valves opens, 
the air being expanded beyond what the column M at rest could 
keep it at, water will be drawn in by P, to be given out the 
next time the valves shut. Were air left in the cylinder, either 
in the bottom of the piston, or between the piston and cover, it 
would cause a halt or pause as the crank turned the centre, at 
top and bottom, for the air would be alternately condensed and 
dilated by the pressure of the upper, and the suction of the un- 
der column. Hence, a space of time would elapse before their 
combined effects were felt by the piston, and there would also be 
wasted, every half stroke, the quantity of v'ater that A supplied 
VOL. in. xo, 5. .ruLY 1820. ' 
M 
