Some of London's telephone operators and engineers, trying out their gas masks at the anti-gas civilian training centre in Gloucester, where they were taught how to deal with gas attacks. (Photo by Harry Todd/Fox Photos/Getty Images). 13th February 1937

Shoppers wrestle over a television as they compete to purchase retail items on “Black Friday” at an Asda superstore in Wembley, north London November 28, 2014. Britain's high streets, malls and online sites were awash with discounts on Friday as more retailers than ever embraced U.S.-style “Black Friday” promotions, seeking to kickstart trading in the key Christmas period. In the United States the Friday following the Thanksgiving Day holiday is called Black Friday because spending usually surges and indicates the point at which American retailers begin to turn a profit for the year, or go “into the black”. (Photo by Luke MacGregor/Reuters)

This incredible panoramic photographs are distorted to create miniature worlds and terrifying tunnels. (Photo by Caters News)

Men use ropes to try and right a supply truck overloaded with wheat straw along a road in Dargai, in the Malakand district, about 100 miles northwest of Pakistan's capital Islamabad, on April 13, 2012. (Photo by Mian Khursheed/Reuters)

Pod of dolphins surf effortlessly through the waves in the wild traveling at speeds up to 20 mph. (Photo by Greg Huglin)

People stand along Aviation Blvd. as the space shuttle Endeavour lands at LAX in Los Angeles. (Photo by Wally Skalij/Los Angeles Times/MCT)

People take pictures of huge waves crash on the Viavelez seafront in the northern Spanish region of Asturias January 2, 2016. (Photo by Eloy Alonso/Reuters)