LII
and there is another place, in which heat increases 1° only after
a descent of 444′. These varieties may be caused by cool or
warm waters, the influence of air (e.g. in bores from the top of
a hill), by the conductive property of the rocks, also by chemical
doing processes. Perhaps the centre of heat is also not at the same
distance from every place of the earth's crust. 3. Hot-wells,
(f.e. Geysers in Iceland) which occur even in the coldest parts
of the earth; their heat is constantly the same and greater than
the heat in any part of the earth's crust within our observation.
4. Volcanoes. The heat of lava-streams must be estimated to
amount to 2000°R. We may imagine the excessive heat of lava
from the fact that vessels of glass melted on the table in a mon
astery without coming in contact with the lava itself. A lava
stream still moved after 10 years and another one was so hot
after 3½ a year that pieces of wood thrown into it were melted
at once. 5. Earthquakes. 6. The lifting and sinking of whole
masses of land.—The cause of this excessive heat is: the earth
having formerly been in a melting, fluid state like a great many
at other celestial bodies, is not yet cooled down and in its interior
parts it is still in the liquid state of such bodies.
§ 127. f) Heat due to changes of conditions, —see: 309.
(Heat is set free by solidification and liquefaction § (153–155).
§ 128. g) Heat due to electricity see: § 270. 285.
2) Propagation of Heat.
§ 129. a) Conductive power of bodies. There are good
and bad conductors: Metals and wires are good conductors;
paper, wood, ashes, earth and soot are bad conductors: 266–272.
The worst conductor is air, hence all porous bodies are bad con
ductors. Use of cloths. 273. Ice folded in flannel. 274. Houses
built of wood and ice. 275. Tight and loose dresses. 276. Snow
protects seed and young grain from frost. 277. Water a better
