Cover of the Swiss-Belgian physicist Auguste Piccard's (1884-1953) report on the first balloon flight to enter the stratosphere. The flight, on 27th May 1931, carried Piccard and his assistant Paul Kipfer to a record altitude of 15.781 metres, making them the first people to enter the stratosphere. In order to reach the stratosphere Piccard had designed the gondola to be airtight, with pressurised air inside, and used a very large balloon, that didn't require to be fully inflated for take-off. During the flight they were able to gather substantial data on the upper atmosphere and measure cosmic rays.