Evening star., 1947-08-17
Science Tracks Gales
AT Sea by Measuring
Tiny Earth Waves
By Alton l. BIokesIee
Assoc;cted Press SCIENCE Reporter

Assoeioted Press Science Reporter
NEW YORK, Aug 16.-Even on
the solid earth, man and all his
building constantly ride up and
down on tiny waves only few mil
lionths of an inch high
These waves are one to several
miles apart, but travel at thousands
of miles an hour. Were they big,
they could shake the earth apart in
violent, sickening rocking.
+ These tiny earth waves are called
microseisms. A fascinating story of
how they were used in wartime to
spot and track storms at sea-hun-
dreds to 1000 miles from shore-is
told by the Rev. James B. Macel-
wane, S.J., dean of the st. Louis
University Institute of Geophysical
Technology. in a new book, when
the Earth Quakes."
Some of the earth waves are short,
and some long. The short ones are
about mile long-a mile between
crests. The longer ones come with
crests several miles apart, and the
time between crests is only three to
seven seconds, he explains.
Waves Larger in Winter.
These longer waves are usually
larger in winter than in summer.
But in summer or winter. there are
times when the waves become many
times their normal height, contin-
uing like that for hours or several
days. he said
Scientists theorized they might be
connected with storms at sea. or
with storm waves beating against
rocky coasts, but none knew for GER
tain.
At ST. Louis University, the Rev.
j. E. Ramirez under Dean Mac
Elwane's direction designed special
seismographs-which detect earth
vlbrations-and set them up, far
apart, in pairs in triangular ar
rangement.
This way. they measured the speed
and direction of the waves, and
found that at st. Louis they move
about 1.6 miles per second, or $3.50
miles per hour.
Came From Storm at Sea,
But what was most interesting
about this type of microseism was
that in every case when the waves
rose up to unusual heights, rising
and falling more or less rhythmi-
cally N groups, they were coming
from a storm at sea such as hur-
ricane or ai1 extra tropical (non-
tropicaD storm of great intensity"
The war cut off weather reporting
between ships and land stations. and
ships were endangered by unre-
ported hurricanes or other storms.
The Navy established a microseis-
mic research project. setting up sta
tons in Florida, Cuba, and Puerto
Rico.
1t was found beyond doubt, Dea1
MacElwane said, that hurricanes
and other intense storms set up
microseisms of this long type, ana
the bearing of each storm center
could be measured with accuracy
from each station as soon as the
storm center came within range.
This range varied from some 300
miles for small storms to more
than 1000 miles for storms of great
intensity. Cross bearing from two
or more stations located the storm
center with higher degree of ac-
curacy than is possible by any
other method.
Helps 4to Track Stormss
"Not only did the bearing point
storm center over the ocean
rather than a. coast subjected to
surf, but the microseisms generated
by a sudden development of a storm
were recorded much too soon to al
low the storm waves to travel over
the sea to coast where surf would
be produced"
The method, Dean MacElwane
said. provides a powerful tool to
locate and track storms from the
time they are formed until they
are dissipated or pass inland.
Microseisms form only a small
portion OF Dean MacElwanes story
of this trenohlipp opd obopoipo