XXXIII
§ 77. The Principle of Archimedes see: 169.
That a body in water loses a part of its weight equal to the
weight of the displaced water, was discovered by Archimedes
when in his bath. He then ran home crying: “I have found it
(“eureka')!"
There are many applications of this principle: A dog may
raise the body of a man in water, 170; a stone seems to be
very light in water, 169; we may raise a bucket full of water
with one finger to the surface of the water, 172; man is able
to swim, 173; fishes and their swimming bladder, 174. Fishes
remain in suspension wheresoever they are, they lose in water
the whole of their weight. In consequence of this, will a tumbler
partly filled with water be heavier after some fish have been
thrown into it?
§ 78. By means of Archimedes' principle also the specific
weight of bodies may be determined.
A solid body is at first weighed in air, afterwards in water,
the difference represents the weight of the displaced water, which
has the same volume as the weighed substance. In calculating,
how often this difference or weight of water is contained in the
weight of the substance in air we get the specific weight of that
substance.
To get the specific weight of a liquid, say alcohol, we weigh
a body not dissolved by water or alcohol at first in water and
then in the liquid in question. In finding the loss of weight
in each case and ascertaining how often the loss of weight in
alcohol is contained in the loss of weight in water, the quotient
thus obtained, represents the specific weight of the liquid (alco
hol). Another method is to use a vessel containing a fixed
mass or weight of distilled water, and substituting the liquid in
C
