Good Red Rays

Every navigator loves his sextant. He bought it when he was still at school, paid perhaps $100 for it. When he is signed on a new ship, it is assumed he will bring his own sextant; it is bad nautical manners to borrow another man's. It may be more or less ornate but it is much the same as the sextant that John Hadley invented in 1731.* Every noon at sea he goes up on the bridge and measures the angle the sun and the horizon make in the instrument, which gives him by logarithmic formula his position. When the sun is overcast, his sextant is useless. Last week in Manhattan navigators were impressed by the first major improvement since 1731 in the sextant, demonstrated for the first time in the U. S.

It was the thermoelectric sextant, using infra-red rays, invented by Paul Humphrey Macneil. The infra-red rays are in the long-wave end of the electromagnetic spectrum. They are really heat waves, capable of penetrating clouds. The Macneil Sextant has a curved reflector that collects and potently focuses infra-red rays on a thermocouple, two pieces of metal which when heated even one-millionth of 1DEG give off a tiny flow of electricity. This flow is enormously amplified, measured by a galvanometer. When the curved reflector is pointed directly at the sun, the flow of electricity is greatest and the navigator can "shoot"' the invisible sun.

So impressionable is the instrument that it records even the heatwaves of another ship, a smokestack, an airplane, many miles away; the heat of a man's face a mile away. It not only registers heat waves, but differences of temperature in itself. At night, or in a fog. the electric eye sweeps the horizon. When it encounters an iceberg it loses heat. This loss of heat is recorded, the position of the iceberg determined. Now Macneil is trying to make it record even the infra-red rays from the stars, to chart a ship's position at night.

Inventor Macneil began his pursuit of infra-red rays as an undergraduate at the University of Michigan. During the War he considered how to apply his researches to a nautical instrument, fixed on the sextant. Because no U. S. workmen could make the delicate apparatus required, he went to Holland. In February 1931 he guided the Mauretania across the Atlantic with his thermoelectric sextant, which was later adopted by the British Admiralty. Last week he announced he was ready to begin commercial production. A ship will need but one thermoelectric sextant which will cost about $2,000 instead of $200.

Inventor Macneil was not the only one playing last week with infra-red rays. At Schenectady, General Electric Co. installed in its main office an infra-red drinking fountain. When a drinker lowers his head over the fountain he intercepts the rays and a stream of water is turned on. Drinkers were at first too awed to drink.

*Hadley's device for measuring angular distances was really an octant, employing a graduated arc of one-eighth of a circle. Capt. Campbell enlarged it to one-sixth in 1757 to use it for navigation purposes.

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