XXXII
weight of the displaced liquid will be as heavy as the whole
body; f.e. if A = 2 and C = 3, the body will be buoyed by a
pressure = 1, hence ⅔ only of A being in water will displace a
mass of water sufficient to counterbalance A.
This law can also be proved by experiment; to the scale-pan
of a balance is attached a hollow cylinder and to this again a
solid one fitting exactly into the hollow one; the weight of both
cylinders is counterpoised by weights laid in the other scale-pan.
If the lower solid cylinder is immersed in water the equilibrium
will be disturbed and only by filling the hollow cylinder with
water the two scale-pans are balanced again (see Stewart's
Primer, page 28-3o).
In consequence of this oil swims on water, 156; a hollow
ball of metal floats, 157; but bottles filled with water sink,
158; bodies of people who are drowned rise after some days to
the surface of the water, 159; Buoyancy may be so strong that
a sunken machine can be raised by empty kerosine-casks connect
ed under water with this machine; ice floats in water, 160;
vessels in spite of the heavy cargoes they carry do not sink,
161; men, fastening on air bladders, swim easily, 162; sedi
ments are formed in liquids, 163; some woods sink deeper in
water than others, 164; vessels entering from the ocean the
mouth of a river draw more water, 165; an egg sinks in ordi
nary water, but swims in salt water (the water of the Dead Sea!),
166; iron floats on mercury, but sinks at once in water
(wood-brooks carry along big pieces of rocks).
§ 76. The effects of suspension, immersion and floating
may be well demonstrated by the Cartesian diver, a glass cylin
der, nearly full of water, in which a little hollow figure with a
little hole in it by causing or removing pressure upon the
water will be caused to sink or to rise. Now this law of buoyancy
is called:
