Bellefonte Beacon

Pilots flying the night mail through fog and rain that blanket all ground lights, follow a trail of dots and dashes which flow from radio range-beacons into their earphones. But sounds are sometimes deceiving, subject to radio interference. Skill is required to compare the relative strength of opposing signals. And at 15-minute intervals the guiding stream of signals are interrupted completely for broadcast weather reports.

For better guidance, the research division of the aeronautics branch, Department of Commerce, has spent three years in developing a device by which the pilot may see his signals. Known as the visual radio range beacon, the invention won public notice last autumn when Lieut. James Harold ("Jimmy") Doolittle made his famed blind flight at Mitchel Field, L. I. (TIME, Oct. 7).

Last week the Department of Commerce announced a visual beacon will be erected at Bellefonte, Pa., in the middle of dread "Hell's Stretch" (graveyard of many a mail ship), for tests by NAT pilots on the New York-Cleveland run.

Visual radio signals are received in a box mounted on the plane's instrument board, containing two white-tipped metal strips called "reeds." The reeds, placed side by side, vibrate vertically in tune with the two modulation frequencies used by the sending station. The "longer" reed (i. e., the one which looks longer because it vibrates with greater intensity) indicates the side on which the plane is off its course.

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