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PBS News Hour / YouTube

The world's largest instrument exists deep inside the Luray Caverns in the Appalachian Mountains, and it's 400 million years in the making, Scientific American reports. It's called the Great Stalacpipe Organ, but it's unlike a typical organ, which forces air through pipes to create music — this instrument rhythmically strikes the cave's stalactites to create beautiful sounds.

How it works: Large, rubber mallets sit next to the 37 stalactites. When the organist strikes a key on the instrument, the corresponding mallet strikes the stalactites, all coordinated via a hidden mechanical device that receives electrical signals from the organ. The organ's inventor sanded down 35 of the 37 stalactites to perfect their tone (two didn't need it) and the 3.5-acre cave lends natural acoustics for the songs.

Because the acoustics are not uniform throughout the cavern, it can be difficult to play by ear. So an automated system — using a plastic sheet with holes in it that rotates around a metal drum — plays songs similar to a player piano. When the metal meets the drum, corresponding stalactites sound off.

Go deeper: A combination of Mother Nature's work, time and a skilled mathematician helped create the Great Stalacpipe Organ. The large, echoey chambers of Luray Caverns have formed naturally over the past 400 millions years. Calcium-rich water droplets eventually formed the large stalactites that hang from the cave's ceiling and now act as an integral part of this instrument. Back in 1954, mathematician and electronics engineer Leland Sprinkle visited the caverns. As was customary during these tours, the guide would strike the stalactites to show visitors how each one gave off a unique sound. That moment sparked an idea in Sprinkle's head — create the Great Stalacpipe Organ, which he did in three years.

Go deeper

Narrowing the employee divide

Illustration: Shoshana Gordon/Axios

Companies are narrowing the blue- and white-collar experience as they're forced to adapt to a worker-led market.

Driving the news: Basic office tools and concepts like corporate communications and schedule flexibility are migrating to frontline operations through investments in technology.

2 hours ago - Health

U.S. to buy 500 million more Pfizer doses to share with the world

A nurse fills a syringe with a dose of the Pfizer-BioNTech COVID-19 vaccine. Photo: Ben Hasty/MediaNews Group/Reading Eagle via Getty Images

The Biden administration is planning to purchase 500 million more Pfizer-BioNTech coronavirus vaccine doses to donate to the world, officials said in an op-ed Wednesday.

Why it matters: The move represents a big step toward making the U.S. a major global vaccine supplier just as China has ramped up exports of its Sinopharm, Sinovac and CanSino vaccines, which can be stored at normal refrigerator temperatures.

D.C.'s building boom grinds to a halt

Illustration: Brendan Lynch/Axios

The decades-long building boom that remade Washington D.C. is screeching to a halt, undone by broader construction trends and the legacy of the post-pandemic workplace.

Why it matters: Dizzying construction has reshaped the city, reinvigorated downtown and created bustling new communities.