Evening star., 1949-07-15
High Tides in Solid Earth
Measured BY Navy Stuff
DR.. Zerbe Reports on Measurements
Made in Basin Near Cabin John
Bv Thomas r. Henry

By Thomas r. Henry
High tides in the solid earth underfoot
may reach an altitude of as much as a
2000th of an inch.
Perhaps the most precise measurements
yet made of earth tides-the surface of the
earth rises and falls due to the gravitational
pull of moon and sun just like the surface
of the sea-have just been reported to the
American Geophysical Union here by DR..
w. B. Zerbe of the Navys research staff.
Near Cabin John the Navy maintains the
David Taylor model basin-a water filled
basin for testing ship models. The dimen-
sions Of the basin and the amount of water
it contains can be measured with great ac-
curacy. The degree of pull of the sun and
moon on water also have been precisely
calculated.
What Calculations Show.
DR.. Zerbe's measurements however,
showed that the extremely small tides which
occur in the basin, with an average range OF
about -thousandths of an inch a day,
still were somewhat larger than those deter
mined by the gravitational pull on the wa
ter surface alone. The difference was about
1,000th Of an inch-part of which must be
due to the rising and falling of the earth's
surface under the water.
Here the problem became extremely COM
due to quite different cause. the fitting of
the earths surface under the weight of high
ocean tides piling up on the beaches. Calcu-
lations showed that this might account for
slightly more than half the observed dis
crepancy. The solid earth tides must be re-
sponsible for all the rest.
That earth tides exist long has been obvi-
Gus to geophyscists but the difficulty OF
measuring them has been so great that only
lot;o oF -
earth's rise and fall have been possible.
Three kinds of synthetic fog, closely du-
plicating the types found in nature. are be-
ing produced by University of California
scientists.
Started in cooperation with the Navy
late in the war. the ultimate object of the
work is to devise means of fog dispersal
over air fields. There are however, several
other military applications, one of which is
the observation of objects by means of
fog screen which may be- more extensive
and far less obvious to the enemy than .
smoke screen.
Accurate measurements are being made
of light transmission through fog and of the
visibility of automobile headlights. aircraft
beacons and railroad and highway signals
Due to Different Causes.
The three kinds of fog may be similar in
their superficial appearance, the University
of California scientists explain, but they
are due to different natural phenomena,
all of which can be duplicated in the fog
machine they have set up.
First there is radiation fog which oc-
ours in valleys. 1t is formed when air loses
heat to the ground through radiation, re-
sulting in vapor condensation. Second is ad-
vection fog, formed when warm air from a
body of water drifts in and mixes with air
over a cold area. Third is the type occurring
on hill SUBMITS which is formed when
saturated air mass moves up hill and the
air temperature drops sharply.
The fog machine is essentially double
walled tank equipped with windows for
observation and photography. Cold or warm
moist air is introduced into the tank from
a. connecting vapor tank Within the tank
the saturated air can be cooled or heated by
the circulation of warm or cold water in
the jacket.
Advection fog. for example, can be gen.
Grated by sudden mixing of warm satu-
rated air from the vapor tank with a cool
air mass in the fog tank.