Unsecret Weapon

SCIENCE

Last December, as London lay almost helpless under Nazi air attacks by night, Air Chief Marshal Sir Hugh ("Stuffy") Dowding predicted with mysterious confidence, "Night bombing will be greatly reduced by spring." Since then repeated reports have come from England of Nazi raiders brought down in full darkness. Last week a clue to this amazing prediction and promise of fulfillment was provided by the U. S. Patent Office.

It granted to Joseph Lyman of Huntington, N. Y. a patent for a machine which uses radio beams to locate a plane in darkness or fog, plot its course through the skies on an indicator like a television screen. Anti-aircraft fire can thus be directed, it is thought, with even more accuracy than in present daylight firing.

Lyman's device uses very short radio waves* which can be focused by parabolic reflectors into beams. (The shorter the waves, the better they can be focused.) Directed into space, the beam will bounce back if it hits metal. Lyman's device rapidly combs the skies with directed beams, picks up reflected signals with a coordinated parabolic receiver. Returning signals are shown by a spot of light in a cathode ray tube (heart of television receivers). The moving spot charts the course of the plane.

Such signals do not distinguish defending from attacking planes. So AA. men must be sure the dark sky is clear of their own planes before opening up. Presumably the device is also adaptable for use by defending planes, which can feel out the murk with radio beams coordinated with their machine guns.

Joseph Lyman's invention was supposed to be a big secret. But details were still available to anyone at the U. S. Patent Office this week, while Science Service discussed it.

* Of 600 megacycles--or about 50 centimetres from trough to trough of the radio wave.

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