Science: Seisms & Sferics

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Englishmen admit that dirty weather won at least half the battle for England when Spain went down with the Armada in 1588. Dirty weather — under the guise of Kamikaze, the Divine Wind — saved Japan from defeat in 1274 when Kubla Khan's invasion boats were smashed to flotsam. Dirty weather postponed and al most disrupted World War II's Dday. In peace or war, weather is important, and these days of air travel reliable weather information is more important than ever before.

The Army & Navy have finally taken the wraps off two wartime improvisations which are proving valuable aids to the still not-too-exact science of aerology.

The Navy's new method of spotting hurricanes is to keep tabs on "microseisms," the tiny vibrations which continually shake the earth even when the motion cannot be traced to an earthquake. Seismologists have suspected for years that microseisms might be started by vio lent storms, which generally reduce atmospheric pressure, and so take a load off the earth, which then expands slightly under the storm centers.

After experiments in St. Louis, a pilot station was set up at Guantánamo Bay, Cuba, in 1944. A battery of three seismographs was arranged in a three-cornered pattern. These indicators measured the strength and nearness of the tremors set up by several full-fledged hurricanes which roared past Cuba that season. Results were good. This year the Navy established two more stations, one in Florida, one in Puerto Rico, to keep a triangulated finger squarely on storms in the Caribbean hurricane belt.

The Army used what it called "Sferic" — Static Direction Finder — a device developed in Florida and combat-tested in the storm-ridden Pacific theater. Sferic employs a radar-like directional antenna (two mutually perpendicular receiving loops) and cathode-ray tube. Certain types of storms are accompanied by severe electrical disturbances, familiar to every radio listener as the crashing static that accompanies a thunderstorm.

Sferic's antenna, revolving like a non stop merry-go-round, seeks out these static signals and relays them to the weatherman as straight-line flashes on the face of the cathode-ray tube. The angular positions of the flashes indicate the di rection the storm is taking. A network of stations taking simultaneous observations of the same flashes can locate their source and spot a storm position in a 2,000-mile radius. One drawback: not all storms stir up enough static.