1178
THEORY AND PRACTICE OF ENGINEERING.
Rook II.
the nozzle determined by its own size : -j'g of the difference between the jet to be madeand the end of the branch is set upon each side the diameter of the upper end of thebranch ; a straight line is then drawn across, and an arc of a circle described on it, from theextremity of each end of the diameter of the jet, until it meets the top of the branch : thejet is then continued parallel, the length of its own diameter ; the metal is carried £ of aninch above this, which allows a hollow to be turned on its edge.
The size of the jet on the inside is proportioned by making its diameter | of an inch forevery inch in the diameter of the cylinder, for each 8-inch stroke : when the water is tobe carried to a greater height, a jet whose area is if less is made use of, with a branch from4 to 5 feet in length. The following table will show how the water acts upon the surfaceof the water in the air-vessel.
Height of
Height of
Ratio of the
Height towhich theWater willspout.
Water in the
the com-
Air’s Elas-
Air-vessel.
pressed Air.
ticity.
h
i
5
2
33
3
h
3
66
3
?
I
4
99
4
3
5
132
5
B
6
165
6
7
7
198
!
Height ofWater in theAir-vessel,
Height ofthe com-pressed Air.
Ratio of theAir’s Elas-ticity .
Height towhich theWater willspout.
7
8
S
8
231
8
h
9
269
TO
T5
10
297
n
n
n
(a-l) 33
The common Garden F.nyine is made in a variety of forms, and with pipes, pistons, air-chambers like that already described; in some the working barrel is placed on the outside,and in others the wooden case is dispensed with.
Fig. 1793.
THE COMMON GABDEN ENGINE,
Another form of this engine will show the sort of pump sometimes adopted for throwingup water from one level to another: but among machines employed for such purposes, pumpsare the most convenient,
as they can be made f
readily to vary the heightto which the water can bethrown, as well as to oc-cupy the least space in theinterior of a cofferdam : thebody of such a pump is theprolongation of an air-tube,and the motion is usuallycommunicated by men act-ing on a balance.
M. Boistard, who has re-corded the useful effect ofthe pump, observes thatone 27 centimetres in dia-meter, (10 *6 inches English )worked by seven men foreight hours, raised 508*52cube metres of water 3*628metres in height ; the use-ful product daily attained Fig. 1791. the common garden engine.