Has the Washington Monument shrunk?
Government surveyors have determined a height for the Washington Monument. It's nearly 10 inches shorter than what has been thought for more than 130 years.
The measurement puts the monument at 554 feet, 7 and eleven-thirty-seconds of an inch. That is measured from the floor of the main entrance to the top. Ever since the stone obelisk was completed in 1884, however, the historic height has been recorded at 555 feet, 5 and 1/8 inches. It's a number circulated for decades on tours of the capital and in civics classes.
The monument honors the nation's first president.
Could this be a case of an incredible shrinking monument? Has it sunk into the ground more than previously thought?
No, not even close, said the chief scientist at the National Geodetic Survey. The survey conducted the measurement with accuracy to within one millimeter.
Modern international standards come from the Council of Tall Buildings and Urban Habitat. It determines an official guideline for building measurements. They call for a different base point than what was likely used in the 1880s. So said Dru Smith, chief geodesist with the National Geodetic Survey. The standard measures from the lowest open-air pedestrian entrance to the building.
"The building didn't change height because of anything. It is just where you start from," Smith said.
The original measurement was conducted in 1884 by Lt. Col. Thomas Casey. He is believed to have used four brass markers as a base for measurement. Those markers remain in place. They are 9 inches below ground off each corner of the monument. It's possible the markers were at ground level in the past. A new plaza was installed around the monument more recently.
Measurements from the brass markers to the top in 1999 and 2014 essentially reconfirmed the original measurement. They showed the 1884 measurement was done with "incredible accuracy."
The only observable height change was the pyramid-shaped tip. It had been rounded off over time. Surveyors in 1934 also noticed the peak had been rounded. They believed it was due to frequent lightning strikes. The strikes had melted the aluminum tip.
"We were able to determine about 3/8 of an inch had been melted off from the very top," Smith said.
That means the original 1884 measurement, completed with much less sophisticated equipment, was within 3/4 of an inch of the findings from the newest survey. It used the original brass markers as a base point.
The monument was completed in 1884. It was the world's tallest structure until 1889. That's when the Eiffel Tower was built. It remains by far the tallest structure in the nation's capital. The city strictly restricts building heights. Most buildings are shorter than the U.S. Capitol dome, which rises 288 feet.
The new survey was conducted while the monument was wrapped in scaffolding. The restoration work is being done because of a 2011 earthquake. The monument was built on land that used to be underwater. It has sunk about 2.2 inches since 1901.
The National Park Service is the caretaker of the monument. The service has no intention of changing its brochures or description of the height to reflect the new numbers.
"We'll still use the historic height rather than the architectural height, since they're measured from different places," said spokeswoman Jenny Anzelmo-Sarles.
Critical thinking challenge: What changed to effect the official height of the monument?