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Site seeing

Blue Hill Observatory has kept an eye on the sky since 1885

From Blue Hill Observatory on a clear day, one sees 90 miles and four states.

DAVID LYON FOR THE BOSTON GLOBE

From Blue Hill Observatory on a clear day, one sees 90 miles and four states.

MILTON — Blue Hill Observatory program director Don McCasland was downright apologetic about the forecast when we called to check hours for a weekend tour. “Unfortunately,” he said, “the weather is going to be good.”

After years of watching local broadcast meteorologists become positively giddy whenever a storm is approaching, we should have known that the folks at the country’s oldest meteorological observatory with continuous records would find anything less than strong winds and mixed precipitation to be a snooze.

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Massachusetts Institute of Technology graduate Abbott Lawrence Rotch founded his private scientific station for the study of weather and the atmosphere in 1885, and made his first climatological observations on Feb. 1 of that year. He chose the summit of Great Blue Hill in Milton in part because it is the highest peak on the East Coast from Boston to Miami where the Atlantic Ocean is visible.

The mini-castle cylindrical observatory perches 635 feet above sea level, making it about a one-mile trek from the parking lots at the foot of the hill. From the Route 138 north lot, it’s easy to walk up the paved maintenance road, where vehicular traffic is limited. From the Route 138 south lot, it’s a moderate hike through the woods of the Blue Hills Reservation up the Red Dot Trail before intersecting the road. The left fork of the trail is a somewhat easier climb with fewer clambers over boulders.

McCasland shares guide duties with several volunteers, all of whom are enthusiastic about this little slice of US and scientific history that became a National Historic Landmark in 1989. “This is the cradle of meteorology,” said McCasland, warming to his spiel. “We have an unbroken climate record inscribed by hand every day. The temperature is taken from exactly the same spot using the same kind of instruments. That consistency is unique in the world.”

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The tour begins in what is almost a trophy room of Victorian-era scientific instruments, many of which remain state- of-the-art. The Campbell-Stokes recorder, for example, measures sunlight intensity from spots burned on paper charts when the sun’s rays shine through a pure quartz sphere. Bound books on the shelves contain the meticulously handwritten observations from across the decades. (The warmest temperature ever recorded was 101 degrees Fahrenheit on Aug. 10, 1949, and on Aug. 2, 1975. The lowest was 21 below zero on Feb. 9, 1934.) Wall displays recount the observatory’s pioneering work in using weather balloons. It was also the first place to use kites to haul equipment into the atmosphere and did some of the first experiments with weather radar.

Old meets new on the next level up, where the oldest mercury barometer in continuous use (since Jan. 1, 1888) shares space with a battery of computers and chart printers. “We do the old homogeneous records,” McCasland said, “but we also have the newest equipment.” The charts make continuous records from some of the remote instruments, notably measuring wind speed, gusts, and direction. They provide around-the-clock records.

In the early years, the observatory took readings every hour. Over time, it became obvious that conditions change too slowly to require that frequency. Now human observers make their official notations three times a day, at 7 and 10 a.m., and 1 p.m.

The observers climb onto the roof (671 feet above sea level) to record cloud types, optical phenomena such as rainbows or sun dogs, and visibility. On a clear day, “there’s a 90-mile visibility and you can see four states,” McCasland said. “Foggy visibility is also exciting,” he enthused, by way of dismissing the pea-soup fog that would soon burn off.

To weather buffs, even a soggy stratocumulus cloud has a silver lining.

Blue Hill Observatory  Great Blue Hill, Milton, 617-696-0562, www.bluehill.org. Open Presidents’ Day weekend-December, Sat-Sun and Mon holidays 10 a.m.-4 p.m., January to mid-February, Sat only 10-4, except Jan. 1 noon-4. Any day by appointment. Overview tours (20 minutes) adults $4, ages 5-17 $2; in-depth tours (45-60 minutes) at 10:30 and 11:30 a.m., 12:45, 2, and 3 p.m (Sun only mid-February to December) adults $8, 5-17 and over age 60 $5.

One in a series on National Historic

Landmarks in New England.

Patricia Harris and David Lyon can be reached at harris.lyon@verizon.net.
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