Evening star. [volume] (Washington, D.C.) 1854-1972, 1932-05-29

a depth of IL miles. The cost of the project
s25 OOOo 900 to 500 900 900, and the time
required so to IS years. would be Offset
according to Parsons, by the unlimited energy
to be obtained from hot rocks at that depth
1t has been estimated that the circulating air
in the Village Deep mine at Johannesburg
South Africa, is hot enough at 1900 feet to
generate 5000 horsepower.
However, the general theory concerning the
internal heat of the earth has undergone radi
cal changes in recent years. The prevalent
hypothesis has the heat originating at mod
crate depths chiefly through radioactivity
aided and abetted by chemical action such as
the oxidation of iron and friction due to slip
ping Of rocks.
THE heat from radioactive materials cannot
! be found at greater depth than IL miles,
according to Samuel G. Gordon, associate
curator of mineralcgy Of the Academy of Nat
ural Sciences, Philadelphia, who has made q
study of radioactive minerals. He reveals that
such minerals are found only in the granite
layer of the earth and this extends to q depth
of only IL miles.
THE interior of the earth as we know it
today consists of series of shells Of different
materials" said Gordon. The upper crust.
with a general composition of granite has q
thickness of some IL miles. 1t is only in this
granite layer comprising the first dozen miles
of the earth's crust that radioactive minerals
are found. Such minerals are found in all
granite rock, and since they are continually
throwing off energy they are source OF con-
slant heat. This activity offers a means OF
determining the age of the rock, since radium
ultimately reduces to lead and a ratio has been
worked out giving the time necessary for this
radium -to-lead process.
Below this 12-mile crust Of granite b
layer of basat about IS miles in depth. Under
this is shell of peridotite Of some 1000 miles,
and in the center 4000-mile ball of some
very dense material such as iron iron with
nickel, substance analogous with meteorites.
While much of the heat found in the granite
crust may be attributed to radioactive min
erals. there is another cause of internal heat
of which too little is known at present. That
Is the oxidation of iron minerals. Rocks at
great depths are ordinarily hot, but they are
kept from melting by the enormous pressures.
When these pressures are lifted by shifting
or slipping of the earths crust, the rock i'm
mediately becomes liquid"
THE enormous tidal pull of the moon and sun
has a message for those interested in the
construction of the earths interior Accord
ing to Lord Kelvin, the earth must be at least
rigid steel to withstand this terrific
strain. If this ball known as Earth were COM
posed chiefly of molten matter incased in a
thin, hard shell, this tidal pull would warp
and possibly rend to bits this protective COW
ering. But while the earth is rigid, it is also
elastic. scientist in 1918 demonstrated that
the earth has tide, but that it does not ex-
coed nine inches.
The manner in which the earth spins on
its axis also indicates that it has the rigidity
Of steel. The shifting of the earth's poles,
known as the variation of latitude, was pre-
dicted as early as 1755 by the Swiss mathe-
matician Euler. The pole of a perfectly rigid
earth would complete its course around a CEN
trail point in 305 days, but the earths psle
takes 433 days because it yields slightly 10
centrifugal force
(Copyright 1882 as.