Government surveyors have determined a height for the Washington Monument that'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, as 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 about the monument that honors the nation's first president.
So 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, which conducted the measurement with accuracy to within one millimeter.
Modern international standards from the Council of Tall Buildings and Urban Habitat an official guideline for building measurements call for a different base point than what was likely used in the 1880s, 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 conducted in 1884 by Lt. Col. Thomas Casey is believed to have used four brass markers as a base for measurement. Those markers remain in place 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, and "it's clear that what was ground level has changed over the years," Smith said.
Measurements from the brass markers to the top in 1999 and 2014 essentially reconfirmed the original measurement, showing the 1884 measurement was done with "incredible accuracy."
The only observable height change was the pyramid-shaped tip, which had been rounded off over time. Surveyors in 1934 also noticed the peak had been rounded and believed it was due to frequent lightning strikes that melted the aluminum tip.
"Well, this time around, we took very careful measurements," Smith said. "We were able to determine about 3/8 of an inch had been melted off from the very top."
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, using the original brass markers as a base point.
"It's remarkable, quite honestly, that they had the ability to get such an accurate measurement back in that time," Smith said.
When the monument was completed in 1884, it was the world's tallest structure until 1889 when the Eiffel Tower was built. It remains by far the tallest structure in the nation's capital, which 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 for restoration work following a 2011 earthquake. Earlier survey results showed the monument did not sink any further into the ground as a result of the 5.8-magnitude earthquake. The monument was built on land that used to be underwater, and it has sunk about 2.2 inches since 1901.
Lest anyone be confused by the changing measurements, the National Park Service as caretaker of the monument has no intention of changing its brochures or description of the height to reflect the new numbers.
"For our purposes we'll still use the historic height rather than the architectural height, since they're measured from different places," said spokeswoman Jenny Anzelmo-Sarles.
The extensive survey will give the Park Service new data as a baseline to track any changes in the monument's height, tilt or compression in the future.
"I think we can all agree the significance of the Washington Monument is really far greater than the architectural qualities or even its height," said Mike Commisso, a cultural resources specialist for the National Mall.
"It continues to serve as a memorial to one of the most influential and prominent public figures in our nation's history."
Critical thinking challenge: What changed to effect the official height of the monument?