LIX
dulum. In § 56, a, (136); we read about the influence of
temperature upon a pendulum. To compensate for these changes
a pendulum was constructed, in which the evil corrects and cures
itself. For this purpose the several metal bars, of which the
pendulum consists, are arranged in such a manner, that the up
ward expansion of some rods is exactly compensated by the
downward expansion of some other rods.
§143. b) Εxpansion of Liquids. They are more ex
pansible than solids.There is the remarkable exception that
water at 4°C has its maximum density, and if still cooled down
it expands. Great importance of this fact in the economy of
nature. 291. 295 and 296. An evident proof of design in na-
ture! Applications are: A tumbler full of water runs over when
the water is heated. 297. Mercury in the thermometer. 298.
§ 144. c) Εxpansion of Gases. Their expansion is most
regular and their expansibility is even 13 times as great as that
of water.
§ 145. As to the expansion of vapours it is the greater
the more vapours of the same density are heated or the more
they are condensed by pressure, but this pressure cannot be in
creased ad libitum, for, having obtained a certain density, va
pours will enter the liquid state. A vapour in this maximum of
density is said to be saturated and in this state it has also ob
tained the maximum of expansion. For the vapours of dif
ferent liquids the maximum of expansion differs, but the ex
pansion of vapours coming to existanee by ebullition is the same
for all liquids, it is equal to one atmosphere.
Applications are: The skin of chest-nuts bursts in the fire,
299; the crackling of fire-wood, 300; the bladder on a hot
metal plate, 301; a tumbler held over the flame of a candle
and then put on the hand, 302 (scarification); smoke rising,
