Sky Thermometer

It was a balmy spring night, but the thermometer read well below freezing. The thermometer, in a professor's backyard garden at Raleigh, N.C., was measuring the temperature of the sky. Together with an ordinary thermometer and an anemometer (to measure wind velocity) it was also giving an accurate forecast of local weather for the night.

The device, an invention of Professor Charles M. Heck, head of the physics department at North Carolina's State College, in effect plucks down the sky's low temperature and focuses it on the thermometer. How it works: the polished aluminum surface of a small cone surrounding the thermometer radiates its heat to the sky but is protected from the ground heat by the nest of twelve larger cones with air insulation between them. The innermost cone thus cools to sky temperature, and the thermometer with it. Temperatures as low as --20DEG F. have been recorded even in North Carolina.

When the sky is absolutely clear, radiation from the ground is maximum, and the thermometer should theoretically go down to 60 below or less. Actually a drop of 47DEG below ground temperature is the greatest yet recorded. On a foggy night the moisture blanket prevents radiation and there is no drop in the thermometer. On a partly cloudy night the thermometer records the passage of clouds, rises as much as 20DEG within four minutes when a cloud passes over. The molecules of water in the air, whether as droplets or as invisible humidity, reflect heat waves from the ground and give higher readings on the thermometer.

Upper-Air Mirror. Physicist Heck's nested cones have vast potentialities for supplementing planes and meteorological balloons for getting upper-air readings for accurate weather forecasting.

The sky thermometer can tell within half an hour after sunset how cold it will be by morning. It draws a running picture of the clouds that pass overhead, records breaks and thickenings. It also indicates upper-air humidity, precursor of cloud patches the next day.

The operator of Heck's cones can also calculate the rate of approach and intensity of warm and cold air masses, basis of all modern forecasting. But it would take many a Heck thermometer, scattered far & wide on land and ships at sea, to give the readings that air-mass analysts need for accurate forecasts for farmers, airmen, generals. For local readings, useful to pilots and battlefront command, it is portable, easy to install. It is not in war use. So far Professor Heck, true scientist, is just "having a lot of fun with it."

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