In 1924 the British made another attempt on Everest, and the world altitude record was again broken. On 4 June, Edward Norton, without supplemental oxygen, reached a point on the mountain's Great Couloir high, his companion Howard Somervell having turned around a short distance before. This was an altitude record which would not be broken, with certainty, until the 1950s, or without supplemental oxygen until 1978. Three days later George Mallory and Andrew Irvine disappeared while making their own attempt on the summit. There has been much debate over whether they reached a greater height than Norton, or even the summit, but as there is no direct proof they are not generally credited with a record.