Discovery of cosmic rays (Victor F. Hess)

On 7 August 1912 the Austrian physicist Victor Franz Hess (1883–1964) took a balloon flight during which made some breakthrough measurements that led to the discovery of cosmic rays. Hess was awarded the Nobel Prize for his discovery in 1936. To mark the one hundredth anniversary of this event a memorial plaque was unveiled in August 2012 at the Jan Evangelista Purkyně University.

Hess, then a twenty-nine-year-old assistant at the Radioactivity Research Institute of the Imperial Academy of Sciences in Vienna, had been engaged in practical measurement of the earth's radioactivity since April 1912, as part of which he took a number of balloon flights. He always took off from Vienna, but the coal-gas-filled balloons did not allow him to ascend higher than 3 000 m. This was not enough for him and so he decided to take a flight to a greater altitude, which meant changing the coal gas for hydrogen. Hess therefore contacted the Austrian Association for Chemical and Metallurgical Production in Ústí nad Labem (now Spolchemie) and that enterprise promised to provide him with the hydrogen he needed.

The new take-off point thus became Ústí nad Labem, near which was also the German Aeronautical Association in Bohemia (in Teplice-Šanov), which provided a balloon called Böhmen. He took off on 7 August 1912 at 6:12, apparently from the actual chemical plant site between Ústí and Předlice. Besides Hess, the three-man crew also comprised a pilot and meteorologist. The balloon ascended to a height of 5350 m and after a six-hour flight landed near the village of Pieskow, some 50 km from Berlin. During the flight Hess measured changes in the electrical conductivity of the air and found that this conductivity was caused by sources of ionizing radiation beyond the Earth's atmosphere. As the intensity increased proportionately to the height above sea level, he concluded that the radiation was not of terrestrial origin, and could only originate in space. Hess’s discovery was of enormous importance for the further development of elementary particle physics and Hess received the Nobel Prize for Physics in 1936.

The memorial plaque at the Ústí University is the work of the local artist Karel Hájek. The plaque is in an unusual balloon shape. It commemorates the event for which the balloon and hydrogen provided by the local associations played a key role.

Krsek, M.: Šedesát ústeckých NEJ. Ústí nad Labem 2007.
Krsek, M.: 100 let od objevu kosmického záření. Ústecký sborník historický = Aussiger historische Zeitschrift 2012, č. 1–2, s. 141–143. 
100 let od kosmického záření. URL: http://www.rozhlas.cz/planetarium/priroda/_zprava/1093738 [30. 11. 2018].

Victor Hess in the basket of a balloon just before take-off near Vienna (1911). (Author: public domain)

A commemorative plaque on the campus of the University of Ústí nad Labem commemorates the discovery. (Author: jam)