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be preceded by the laborious separation of it from
ordinary hydrogen; but if it were possible easily to
"burn" ordinary hydrogen, sooner or later some mad-
man, or perhaps a disappointed would-be world-dic-
tator, would set fire to the sea in such an uncontrollable
way that the wave of burning would consume all the
hydrogen on the earth. A rough calculation shows that
the energy would be enough to make the earth shine
for more than ten years as brightly as the sun does now.*
It would make the solar system into a very respectable
new star. On the whole it is very satisfactory that we are
never likely to be able to "burn" our hydrogen.
Finally, there is a conceivable source of energy in the
* For this kind of calculation it is convenient to use the prin-
ciple of relativity and count energy by its weight in tons. The sun
radiates four million tons of energy every second. To estimate
the amount of hydrogen on the earth, I assume that the sea holds
most of it. The amount of water in the sea has been estimated at
about 1.4 x 1018 tons. One-ninth of this weight is hydrogen,
and of each atom of hydrogen eight parts in a thousand are avail-
able for atomic energy. The result is 1.2 x 1015 tons of energy,
or as much as is given by the sun in three hundred million seconds,
which is about ten years.
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THE NEXT MILLION YEARS
annihilation of matter. This would give a supply hun-
dreds of times more potent than the "burning" of
hydrogen into helium, and it would presumably be
hundreds of times more devastating, but it is quite un-
known whether it can happen at all, even in the hot
interiors of stars. It is safe to say that long before this
source could be used, some of the milder forms of
atomic energy would either have been made available,
or else would have destroyed the world.
Since the prospect of getting atomic power on a really
large scale seems not very good, and since water power,
which is much the most straightforward source of
energy, is going to be inadequate, it is important to
consider what other sources might be exploited. Possible
sources, in addition to vegetation, are the direct use of
sunlight, wind, tides, the interior heat of the earth, and
the cold water at the bottom of the sea. Some of these
can never provide large powers, and others suffer front
being very diffuse in their distribution, but they all
deserve consideration.
The internal heat of the earth is already being ex-
ploited at an installation in Italy, where steam is raised
by pumping water into hot fissures in the earth. There
may be other places where this could be done, though
it is hardly likely to be on a large scale. Indeed in prin-
ciple it would be possible to use any volcano as the fur-
nace of a power station, but it is hardly a practical
proposition in view of the unreliable habits of volcanoes.
The existence of volcanoes is attributed to deep cracks
in the ground, which at irregular intervals of time let in
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MATERIAL CONDITIONS
water to a depth, where it is boiled under pressure so
that it explodes out again. This suggests the possibility
that man might directly tap this source of heat by, so to
speak, making artificial volcanoes which he controlled
so that they never reached the surface. Heat does not
flow out from the centre of the earth very fast, and
nothing that man might do could affect this rate, since
he can only hope to work on the outermost few miles
of the earth's shell. Estimated on a world scale the total
energy available is not very great, and the best he could
hope for would be to make a few deep borings and raise
steam in them. He might hope to keep these borings
under control, but even if he was successful in this, there
would still be a price to pay, for his disturbance of the
temperatures in the earth's shell would almost certainly
sooner or later lead to earthquakes. In the light of these
considerations not much can be expected from the
earth's internal heat, beyond a few more stations like the
one in Italy.
An experimental installation has been set up, or at any
rate proposed, with the aim of deriving power from the
difference in temperature between the surface water of
the sea and the water at the bottom. Wherever there is
any temperature difference it is theoretically possible to
get power from it, but the amount depends on the
magnitude of this difference. In the depths of the oceans
in all latitudes the water is only a degree or two above
freezing, and in the tropics at the surface it is perhaps
80° F., so that there is no great margin to work on, and
enormous quantities of water would have to be handled
to get any reasonable amount of power. The possibility
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THE NEXT MILLION YEARS
of this power is guaranteed by basic theory, but I do not
know what mechanism would actually realize it. It
would only be feasible to tap this source in special places,
such as tropical oceanic islands, for only in such places
would there be a high surface temperature together with
proximity to the cold ocean depths. It may be con-
jectured that this source of energy would be too expen-
sive to be much used.
The wind blows on account of unequal heating of
different parts of the earth, so that its energy is derived
from sunlight, like that of water-power or of the fuels
we are now burning up. It could provide considerable [ Pobierz całość w formacie PDF ]