Radiation v. Fog

If they had an apparatus which would show, on a sort of artificial horizon, every object for a mile around, together with its distance and direction, ship captains nosing uneasily ahead through a fog would be much safer and happier. So far such a mariner's boon has not appeared. Yet it seems to be on the way, because the problem is simply one of technical ingenuity in applying principles already understood.

Visible light does not penetrate thick fog, but visible light is only a small segment on the wide spectrum of electro-magnetic radiation. Radiation which is too long in wave length to be seen, called infra-red and embracing wireless waves of all lengths, has the faculty of sliding around obstacles such as fog particles. Therefore an artificial eye which "sees" by infra-red radiation appears to offer the best hope of piercing fog.

Four years ago Commander Paul Humphrey Macneil demonstrated a fog-eye which made use of infra-red radiation in the region of heat waves, naturally emitted by all objects warmer than absolute zero (TIME, May 8, 1933). It turned on warning lights, rang a gong when a fog-shrouded vessel passed another ship. Few months later Master Mariner Flavel M. Williams installed on the Manhattan and Washington a camera which took a picture of an obstacle through fog by infra-red radiation, producing the developed film 30 seconds after exposure (TIME, Jan. 15, 1934).

Last week the talk among communication engineers was of a new fog-eye which, instead of simply signaling, obtains a picture like the Williams device but does so immediately. Patented by Clarence W. Hansell of Rocky Point, N. Y. and assigned to Radio Corp. of America, the apparatus emits radio waves so short that some of them bounce back from an obstacle to the sending point, where they are focused so as to create a tiny image on a copper sulfate screen.* The picture emerges as a white silhouette on a blue background. If the obstacle is a ship, its distance can be inferred from the size of the image.

*As Inventor Hansell last week explained in his own words: "The process of forming the image takes advantage of the effect of integration or accumulation of the effect of the waves upon the screen and this increases its sensitivity."

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