The year 1892 brought atmospheric research the instrument it needed to explore the upper atmosphere: the sounding balloon. Its inventor, Gustave Hermite, had a simple idea: launching "unmanned" balloons. In other words balloons without a pilot, yet equipped with recording instruments, which had to be recovered once they fell back to earth. The first task logically consisted in launching small balloons and verifying if it were possible, in a still very rural France, to retrieve them quickly.

Launching the balloon Aérophile, in 1893

Aerological expedition on board of the ship Otaria, in the 1900's (Photo Météo-France)

On September 17th 1892, Hermite launched his first paper sounding balloon coated with petroleum and measuring four metres in diameter. On board was a "test mercury barometer" weighing 1.2 kg, which would later be replaced by the meteorograph, a new instrument that measured and recorded the temperature and pressure of the air.

It is thanks to sounding balloons that Teisserenc de Bort discovered that from an altitude of 10 km the temperature stopped decreasing. He thereby revealed the existence of the stratosphere.