General Maurice Gamelin, General Officer commanding the French Armies, is on a four day visit to England. He went to the staff college at Minley and is seen inspecting an anti-tank gun at Aldershot, on June 7, 1939. (Photo by AP Photo)

On the second straight day of record-setting temperatures, Maddy Hacker is hoisted up by friend Jasmine Harper, both of McLean, Virgnia, as they attempt an acrobatic stunt in front of the U.S. Capitol in Washington, U.S., February 21, 2018. (Photo by Kevin Lamarque/Reuters)

A visitor jumps for a photograph on the world's highest and longest glass-bottomed bridge above a valley in Zhangjiajie in China's Hunan Province on August 21, 2016. The bridge, which opened to the public on a trial basis on Saturday, spans 430 meters (1,410 feet) and rises about 300 meters (984 feet) above a valley in a scenic zone, making it the world's highest and longest glass-bottomed bridge according to Chinese state media. (Photo by Fred Dufour/AFP Photo)

Allie Labutis wears a painted “Merica” on her thigh during the fifth annual Made in America Music Festival in Philadelphia, Pennsylvania September 3, 2016. (Photo by Mark Makela/Reuters)

An Indigenous schoolchild dressed in traditional attire takes part in a rally to commemorate Indigenous Resistance Day in Catarina town, Nicaragua October 12, 2016. This holiday coincides with Columbus Day which commemorates Christopher Columbus landing in America in 1492. But rather than celebrating the discovery of the Americas, the Nicaraguans observe Indigenous Resistance Day to celebrate the bravery of the indigenous population in the fight against the Spanish conquistadors. (Photo by Oswaldo Rivas/Reuters)

Strokkur geyser against cloudy sky at sunset. Strokkur is a fountain geyser located in a geothermal area beside the Hvítá River in Iceland in the southwest part of the country, east of Reykjavík. It is one of Iceland's most famous geysers, erupting once every 6–10 minutes. Its usual height is 15–20 m, although it can sometimes erupt up to 40 m high. (Photo by Teatsche Dijkhuis/Getty Images/EyeEm)

The Thufa hill in Reykjavik, Friday, October 28, 2016. Parliamentary elections will be held in Iceland on October 29, 2016, more than 250,000 voters are called to elect the new parliament, 63 members of the Althing parliament. (Photo by Frank Augstein/AP Photo)

Prince Philip, Duke of Edinburgh practicing his bicycle polo technique, Windsor Great Park, Berkshire, 1964. (Photo by Norman Potter/Daily Express/Hulton Archive/Getty Images)