On April 15th, 1875, an aviation catastrophe shook France. Three aviators fainted at high altitude during a balloon flight. Two died, the third woke back while the balloon was descending and succeeded in landing safely. The onboard altimeter indicated that they attained a maximal altitude of 8,600 m. Before their tragic flight, they underwent physiological tests in the hypobaric chamber at the Academy of France, in the laboratory led by Paul Bert (1833-1886). Bert had judged them apt to flight, yet he asked the balloon to be equipped with oxygen flasks with a mouthpiece.