cal Society.

The earth's interior, Dr. Shapley said, is the "third dimension" of
geography. Exploration of the planet's surface soon must cease from
lack of places to explore. Even the upper air is coming to be
reasonably well known scientifically, thanks to instruments sent up
with balloons and to the radio and other investigators who have been
uncovering secrets of upper-air electricity. But the interior of the
earth is still one of the great mysteries. It is a paradox of
astronomy that much more is known about the center of the sun or a
star like Sirius than about the center of the earth.

Deep shafts of bore holes into the earth have been suggested often as
sources of heat for human use. It is doubtful, however, whether such
heat supplies could be obtained. For one thing, the supposed internal
heat of the earth is still nothing but a guess. It may be that the
relatively slight increases of heat found as one goes deeper in
existing mines are due to radioactivity in the rocks instead of to
outward seepage from the internal fires. Another difficulty about
utilizing earth heat is that heat moves so slowly through substances
like rock, as any housewife can prove by trying to fry an egg on a
brick placed over a gas flame. As soon as the rock heat immediately at
the bottom of a bore hole had been exhausted heat supply would stop
until more could diffuse in from the sides.

Dr. Shapley's suggestion, in any event, is not to search for heat but
for facts. Even in existing, relatively shallow mines, he believes,
scientific laboratories at different depths under the surface might
yield valuable data not now obtainable. Most scientific men will
agree. Revolutionary as the idea may seem to those familiar only with
the standardized laboratories of physics or chemistry, there are sound
reasons why a half-dozen or so of the sciences should do precisely
what Dr. Shapley suggests.

At least one underground laboratory has already been installed, for
Prof. E. B. Babcock of the University of California has such a
workroom in the Twin Peaks Tunnel, underneath the mountain that rises
above the city of San Francisco. Natural radioactivity in the rocks
thereabouts is greater than normal and Prof. Babcock finds that this
apparently increases new species among fruit flies.

To dig out laboratory rooms a mile or so down in existing deep mines
probably would cost far less than many enterprises already financed by
philanthropists. Even to