There appear to be two small observatories on the roof of the old National Airport terminal building. The spherical observatory structures can still be seen. Are there, or were there ever, telescopes in those spheres?

— Jay Jupiter, Mount Vernon

Not telescopes, but would you believe machine guns? Well don’t.

“Stories go around that during the 1940s, during the war, they were machine gun turrets to protect the capital,” said Mark Richards, the Federal Aviation Administration’s weather site supervisor at National Airport. “Unfortunately, that’s not a true story. There were no machine guns, just people watching balloons.”

The weather station sits atop the old terminal building at the Regan Washington National Airport in Arlington on June 28, 2012. The domes at either end were once used for watching weather ballons ascend. (John Kelly/TWP)

Specifically, weather balloons. The domes did not hold astronomical telescopes. They held theodolites, instruments used to measure angles.

After National Airport opened in 1941, employees from the National Weather Service would regularly fill balloons with helium and release them from the roof of what we today call Terminal A.

The balloons came in different sizes and colors and were classified by their lifting power. A balloon about two feet in diameter could lift 30 grams. They were used to judge how low the clouds were, what’s known as the ceiling. Simply release a red balloon, time how long it takes to disappear into the clouds and, if you know the rate of ascent, you can estimate the ceiling.

Larger pilot balloons — “pibals” for short — could lift 150 grams or more. They were used to judge wind speed and direction, critical information for pilots. During World War II, these tasks were often performed by women.

Mark said the two rooftop domes operated almost like tank turrets. They could be spun around and opened. If the wind was blowing to the north, the observer would position herself in the northernmost dome, looking through the theodolite and recording data on a chart. To the south, she’d stand in the other dome. They provided a modicum of protection from the elements.

“They didn’t have all the fancy computerized equipment we have today,” Mark said. Once a balloon was released, an observer would follow it through the lens of the theodolite, taking a reading every 30 or 60 seconds. “They then could determine that if it got from point A to point B in so much time, the wind had to be blowing from a certain direction at a certain speed.”

Mark said the balloon launches stopped some time in the 1950s. Today, lasers calculate cloud height. Balloons are launched twice a day from the National Weather Service’s Sterling facility and carry instruments that judge wind speed, direction, relative humidity, dew point and temperature.

The office Mark works in — a rectangle atop National’s old terminal, with a dome at each end — has been staffed around the clock for 71 years. Today, only one person is there at a time, pulling an eight-hour shift. He provides weather information to the airport’s tower and monitors the devices that record the official temperature and precipitation for Washington.

The airport’s control tower used to sit on the same roof as the weather office. When a new tower and terminal were built in 1997, the old building was renovated. The domes were removed temporarily. Because the 1941 art deco building is historic, they were refurbished and put back in place. But they no longer rotate or open.

Today, one of the domes is used for storage. The other is a bathroom.

The Bourne ultimatum

In 2010, Answer Man wrote about a tugboat that had sat for two years at anchor in the Potomac near the Woodrow Wilson Bridge. Called the Bourne, the 100-foot-long vessel had done work on the river before being moored, its owner hoping in vain that other jobs would materialize.

Now the Bourne is gone. According to Cmdr. John Burns, former chief of the Coast Guard’s waterways management division for this area, it was towed to Norfolk on June 8. Its final destination is a scrap yard in Texas.

Send a Kid to Camp

As you keep cool this summer, please take time to consider children whose summers mean hot rooms and city streets. These are the kids who deserve Camp Moss Hollow.

Moss Hollow is a summer camp for at-risk youth from the Washington area. For nearly 40 years, readers of The Post have been supporting the camp. You can help, too. To make a tax-deductible donation, go to Click where it says “Give Now,” and designate “Send a Kid to Camp” in the gift information. Or mail a check payable to “Send a Kid to Camp” to Send a Kid to Camp, P.O. Box 96237, Washington, D.C. 20090-6237.

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