CVIII
Water until half of the phosphorus is in water; the air contained
then in the flask has the smell of ozone and acts as such.
§ 271. 4) Atmospheric electricity. By the experiments of
Franklin and Saussure it was proved that electricity is present
in the atmosphere and that lightning and thunder are the effect
of this electricity. The atmosphere always contains free elec
tricity, generally positive, but it is found only at a certain height
above the ground. If water is caused to vaporise in a vessel,
or if vapours by cooling them down are caused to liquify, this
change of temperature combined with the friction between these
vapours and the atoms of the atmosphere produces electricity.
The vapour will show positive, the vessel negative electricity.
In a similar way a change of temperature in the atmosphere
(especially during the formation and reduction of vapours in
the clouds) may cause a separation of the electric tension bet
ween the layers of the atmosphere and the surface of the earth.
Still the matter is not yet cleared up! If a cloud comes within
the electric atmosphere of another one not electric or less
electric, the contrary electricity is produced and a discharge takes
place, which is called lightning. If the discharge takes place
between a cloud and the ground the non-conductors interfering
will be destroyed. When the sky is clouded electricity is some
times positive, sometimes negative, and this may change accord
ing to the passage of clouds. Lighting and its dangerous
discharge. 433. How the zigzag of the lightning is produced
see 436.
§ 272. Also the so-called return-shock may prove very
dangerous and fatal. This is not due to a direct discharge of
a cloud's electricity, but follows such a discharge. As long as
the cloud is near everything like the ground is charged with the
opposite electricity, but after the electricity of the cloud is dis
