Ship-finder

On a cliff 200 feet above the sea stand the two towers of Navesink Lighthouse Station, near Atlantic Highlands, N. J.

One dark, still night last week sentries guarded the lonely road to the Navesink station. No wisp of fog was in the air.

Pricking the blackness a few miles offshore were the lights of the Coast Guard cutter Pontchartrain, cruising slowly.

Promptly at midnight the Pontchartrain's lights went out and the boat vanished in the night. On the hilltop slick-haired, thin-lipped Captain Lawrence L. Clayton of the U. S. Army Signal Corps and a sergeant bent over an apparatus of which the handful of witnesses, mostly newsmen, could make out little except the vague outline of a cylinder and the dim flicker of electric bulbs. Synchronized with the mechanism was an 800,000,000 candlepower Sperry searchlight mounted on a truck a few feet away.

Captain Clayton straightened up from his fiddling with the device. The sergeant barked: "Light!" Instantly the searchlight bored a narrow, dazzling hole through the darkness over the sea. Three miles away, one mile from where it was last seen, the Pontchartrain gleamed in the centre of the beam.

The searchlight went out. Again & again, while the Pontchartrain moved invisibly to new positions at sea, the searchlight flashed on to impale the craft on the beam's end. Nineteen times the beam struck the cutter amidships. Once it caught only the stern.

Asked a reporter: "Could this device be used to point a gun?'' Replied the officer: "Draw your own conclusions." It was generally understood that this latest military secret works by means of infra-red radiation. Emitted by ships and all other objects, this radiation occupies a place on the spectrum between visible light and radio waves, pierces much farther than light does through fog and haze.

Another report was that two radio engineers named Rodman and Dumont had helped Captain Clayton develop the ship-finder, using a thermocouple. Thermocouples operate on the physical principle that, if two small strips of dissimilar metals are made to form a closed circuit, minute changes in the temperature of the strips set up minute electrical currents, which may be amplified by vacuum tubes and measured. Astronomers use thermocouples to measure the temperatures of stars trillions of miles away.

Thermocouples are activated by infra-red radiation as well as by starlight. It would be possible to put the thermocouple at the focus of a movable parabolic reflector, and to assume, when a peak of electrical activity was noted, that the reflector was trained on some strong source of radiation--such as a metal ship out to sea in the dark. If this is how the Signal Corps' ship-finder works, it differs in no essential detail from the infra-red "Fog-eye" developed by Paul Humphrey Macneil and successfully demonstrated two years ago (TIME, May 8, 1933).

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