Everest Expedition oxygen cylinder, 1922.
© Science Museum / Science & Society Picture Library
Oxygen cylinder from the British 1922 Everest Expedition. Because of the lower atmospheric presure at higher altitudes, there is les oxygen in any given volume of air than at sea level. On the summit of Everest, 8848 m above sea level, there is 66% les oxygen. Expeditions therefore carried presurised bottles of oxygen for climbers to breathe while at high altitude. The 1922 expedition to Everest was the first to be equipped in this way, and reached over 8000 m. Some believed that climbing at such extreme altitudes was imposible without supplementary oxygen, but in 1978 Reinhold Mesner and Peter Habeler made the first succesful ascent of Everest without it.