It is not diflioult to see that the strength of the vessels
or pipes which contain or convey water must be regulated
according to the pressure. ^



HYDROSTATICS. 195

The thickness of pipes to convey water must vary in pro-
portion to the height of the head of water X diameter of
pipe -2- the cohesion of one square inch of the material of
which the pipe is composed.
By experiment it has been found that a cast iron pipe 15
inches diameter and } of an inch thick of metal, will be
sufficiently strong for a head 600 feet high^ A pipe of oak
15 inches diameter and 2 inches thick, is sufficient for a
head of 180 feet. When the material is the same, the
thickness of the material varies with the height of head X
diameter of pipe.
Ex What must be the thickness of a cast iron pipe 10

inches diameter for a head of 360 feet ?

360 X 10 X } , - . 1. *!.. 1
fiOO V 15 ^^ 1^ of an inch thickness.
If the same pipe is to be made of oak, then

360 X 10 X 2
1 QA ^ I g — = 2§ thickness in inches.
When conduit pipes are horizontal and made of lead,
their thicknesses should be 2% 3, 4), 5, 6, 7, d, lines, when
the diameters are 1, y , 2, 3, 4|, 6, 7, inches — and when the
pipes are made of iron, their thickness should l/e 1, 2, 3,
4, 5, 6, 7, 8, lines, when their diameters are 1, 2, 4, 6, 8,
10, 12.
