While many people have enjoyed the view from the top of the Washington Monument in Washington, D.C., only a handful have experienced it from the outside. But it was an on-the-job perk for engineers of the National Institute of Standards and Technology (NIST) who made two trips during the 20th century—albeit 65 years apart—to the pinnacle of the capital’s best-known icon.
The first time was in October 1934 when engineers from the National Bureau of Standards (NBS, the predecessor to NIST) took advantage of scaffolding erected during the monument’s 50th anniversary cleaning and restoration project to carefully examine the gold-plated, platinum-tipped lighting rods and the aluminum cap at its apex. Ironically, the impetus for the obelisk’s major overhaul—and the reason for the scaffolding—came from NBS as well. Earlier in the year, an inspection of the monument’s base by NBS building stone specialist Daniel W. Kessler revealed that a poor distribution of the structure’s 73,663 metric tons (81,200 short tons) created hollow spaces and cracks. His solution was to redistribute the weight of the lower section by filling in the hollows with more elastic mortar than originally used.
Three score and five years after the agency’s initial visit to the summit of the Washington Monument, NIST engineers returned there with a new mission: help the National Geodetic Survey (NGS, a part of the National Oceanic and Atmospheric Administration, or NOAA) make the most-accurate-to-date measurement of the landmark’s height. A 1998 to 2001 restoration project once again surrounded the Washington Monument with scaffolding and provided NGS with the opportunity to temporarily place a Global Positioning System (GPS) receiver atop the pyramid cap. NIST engineers designed, built and installed a special mounting that rigidly held the receiver in place and helped pinpoint the GPS signal.
The resulting measurement set the monument’s height at 169.26 meters (555 feet, 3-5/8 inches), only 3.8 centimeters (1.5 inch) off from the historically declared figure obtained with traditional surveying methods. It also is less than 1 centimeter (0.4 inch) different from the most recent NGS survey performed when scaffolding was erected around the monument so that repairs could be made following the 2011 D.C.-area earthquake.
– Michael E. Newman