XXX
§ 71 Pascal's Law see 149-154.
a) The pressure is transmitted undiminished in all direc
tions. 149.
b) The pressure transmitted is proportional to the height of
the volumes of water; on the bottom of a horizontal vessel it is
equal to the weight of a prism made up of the same liquid, the
base of which is equal to the bottom of the vessel and the height
equal to the distance between the bottom and the liquid's level.
Thus a cask is caused to burst by a tube of full water, 150;
empty bottles at the bottom of the sea are either cracked or fill
ed with water. 153.
c) The pressure is independent of the shape of the vessel
and the quantity but not the height of the liquid. 152.
d) The pressure transmitted is proportional to the extent of
surface exposed to pressure, an application of which law we see
in the Hydraulic press (Water-press or Bramah-press; see
Phys. Primer, page 23). 154.
§ 72. As to the pressure of a liquid on the side-walls of
the vessel it is the same as that of a liquid-prism, the base of
which is equal to the place pressed upon and the height equal
to the distance between the centre of gravity of this place and
the liquid's level.
This law is of great importance for casting up embank
ments, for the construction of sluices, and it holds true also
for the surfaces of bodies dipped in a liquid (the bottom of a
boat, sea-animals, the diving-bell). A consequence of this
pressure side-ways is the turning round of Barker's mill. 151.
3) Buoyancy of liquids and specific weight.
§ 73. As the pressure exerted on a liquid is transmitted in
all directions, a pressure exerted upon the upper layers of a
liquid must cause an equal reaction from below, which upward
pressure is termed the buoyancy of liquids.
