താൾ:CiXIV132a.pdf/382

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LXX

the skin.—This transpiration is hindered by air-tight clothes (on
this account they keep warm), by the saturation of the atmos
phere; fever is moderated by perspiration; by high temperature
or plenty of exercise perspiration is caused; by producing a
draught we cool ourselves.

Remark. Highly interesting phenomena in connection with heat are
the following: water-drops on a red-hot iron plate (Leidenfrost's drops);
ice produced by pouring sulphuric acid (boiling-point-10°) and some drops
of water in a red-hot iron vessel; to dip the hand into melting iron. 341.

CHAPTER XI

ON LIGHT

354–394

A. Light in General.

§ 175. Definition. The two theories about the origin of
light: 1) The emission theory: an imponderable substance is
propagated and penetrates our eye producing there the sensa
tion of vision. 2) The undulatory theory: the rapid vibra
tions of the molecules of an illuminating body are communi
cated to the luminiferous ether (conf. the theories about heat)
and are propagated by this medium in the form of waves to the
eye. Of course this ether must penetrate all bodies and occu
pies the whole universe (besides that it is imponderable). The
emission theory (supported by Newton) cannot explain all phe
nomena. One ray of light may be strengthened, weakened and
darkened by another one, according to the emission theory more
light should only increase the splendour. We may transform
ad libitum light into heat, into mechanical force, magnetism etc.
which shows, that these phenomena are in relation to each other.

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