HYDRAULICS. 
the piston ; which may either be solid, as in 
a forcing-pump, or valved, as in a lifting or 
a sucking pump. This valve may be ap- 
plied to a piston, as well as to that part of 
the pipe which retains the water, that it 
may be within reach of the piston’s action. 
An improvement has been made to this 
valve, by adding a ball of some weight to 
the bottom of the shank, B, and excavating 
the button, in order to reduce its weight in 
proportion : this insures the regular descent 
of the button to its seat. 
The butterfly-valve, exhibited in fig. 14, 
varies from the two former, in having two 
semicircular flaps appended by hinges to a 
bar passing over the centre of the excavated 
piston. This valve is peculiarly eligible, 
because if one part should be stiff, and ad- 
here to the piston, the other will play with 
an increased effect, though not equal to the 
action of both valves. 
The simplest valve with which we are 
acquainted is the sphere, which is made of 
metal, and fits into a semi-spherical cavity 
on the top of the piston or block. When 
the piston (if it be on that) rises, the sphere 
falls into the socket; but when the piston is 
depressed, the rush of water from below 
forces the sphere upwards. The only in- 
convenience attendant upon this valve, which 
is shown at fig. 15, is, that its diameter be- 
ing nearly equal to that of the bore, leaves 
a very narrow passage for the water. This, 
however, might perhaps be obviated, by 
making an excavation in the pipe, as shown 
by the dotted lines, and by driving nails 
through to obstruct the ball from rising too 
high. 
These are the general principles of the 
valves in common use; though we could 
enumerate a great variety, which have all 
been strongly recommended, but in prac- 
tice proved very deficient. We shall there- 
fore proceed with the detail of hydraulic 
machines, commencing with those Which 
supply the place of pumps, by raising water 
to given heights. The most simple, and 
perhaps the most ancient, is the spiral pump 
of Archimedes. It consists of a cylinder of 
wood, about a foot in diameter, and of any 
' length at pleasure : on this a leaden pipe of 
any bore is wound from the bottom to the 
top, spirally. When the bottom of the cy- 
linder revolves in the water, (by means of a 
common winch handle at the top, and of 
a pintle in the centre of its base, which rests 
in a box or step for that purpose below) 
the reclined position, as shown in fig. 16, 
the pipe, and to be carried by the revolu- 
tions of the cylinder completely up to the 
top, where it discharges into a vessel. This, 
however, raises but a small quantity, though 
the height may be indefinite : therefore, 
where such a machine is in use, it will be 
found eligible to have the whole cylinder 
covered with various pipes, like the bands 
in a rope, whereby the quantity of water 
raised would be proportionably increased, 
with very little addition of power: the 
greatest resistance would arise from the 
friction upon the supporting axis, especially 
the lower one under the surface. Some of 
these machines have been worked in strong 
running brooks, by means of water-boards, 
the same as the great wheels in undershot 
mills. 
The lwrn-drum, so called from a number 
of segments passing from the circumference 
of a large flat cylinder to its centre, is an 
easy mode of raising water. The scoops, 
or mouths, by turns dip into the water, and 
as they rise cause it to pass up the horn, or 
segment, until it is discharged into a trough 
placed under the end of the axis, which is 
hollow, and has its pintle fastened to a cross, 
as seen in fig. 17. Such wheels usually work 
with water (or float) boards; and some of 
them have projecting fins, from which rect- 
angular buckets are suspended : these dip 
into the water as the wheel turns, and suc- 
cessively discharge into a trough, by means 
of a pin at A, which causes every bucket as 
it passes to turn to a horizontal instead of 
an erect position. The latter invention is 
ascribed to the Persians. The reader will, 
no doubt, readily perceive that a strong 
current, or other force, is needful to move 
machines so laden as the Persian wheel, it 
sometimes raising near a ton of water in 
each revolution ; and that nothing but the 
necessity for raising water could induce to 
so great a loss of power. When treating of 
Mills and of Pumps, as also of Pneu- 
matics, with which Hydraulics are often 
intimately blended, we shall enlarge more 
on this subject ; for the present concluding 
with the ordinary mode of applying a water 
wheel to pumps, as may be seen at London 
Bridge, and in a great variety of instances, 
where immense quantities are raised by 
means of running water, referring to the 
article Steam-Engine for the operations 
dependant on that power. We have, in 
speaking of Fluids, said much on their pro- 
perties, which the reader will find both 
amusing and instructive : indeed we con- 
occasions the water to enter the bottom of sider this doctrine to be indispensable, as 
