LX
303; current of warm air from the inside to the outside in a
room, 304. 302; use of a chimney on a lamp, 305; draughts
in chimneys, 305; expansion and contraction the cause of all
winds, Land and Sea-Breeze. 307. How the climate of a
country is influenced by its situation in respect to large tracts of
land or water!
§ 146. 3) In connexion with this expansion of liquids and
gases, due to heat, we may also understand the way, in which
liquids are heated. This kind of propagation is called con
vexion. 368. (§ 129. 130.) The same process takes place
in tanks and rivers so slowly, that we cannot observe the circu
lation of water. At night and in the cold seasons the water in
the surface cools down, sinks and the warmer layers of water
rise and after having been cooled sink down too, thus causing
a perpetual movement in the water, which is of the highest im
portance to animals living in water. Without this circulation
of water oxygen would never come down into the depths and
this oxygen must sustain the life of the animals living down
there. Besides, this movement prevents corruption and the
poisoning of the earth. Is all this mere chance? Is it not
rather the trace of a purpose laid down in nature?
II. Changes of the state of bodies by the action of Heat.
§ 147. The process of fusion and ebullition shows, that
heat diminishes cohesion and that in the case of ebullition
this cohesion even is changed into repulsion.
§ 148. 1) Laws of Fusion. a) Fusion begins for one and
the same substance at a certain temperature, which is invariable.
b) From the moment fusion commences the temperature does
not rise until the fusion is complete.
§ 149. Latent Heat is the heat absorbed by the body
during its fusion and it is not indicated by a thermometer. 309.
