The hot air balloon borne experiments of Victor Hess led to the discovery of cosmic rays 100 years ago.
They natural source of high energy particles was discovered on August 7 1912 by the Austrian physicist.
He discovered the rays from a series of experiments conducted while in a hot air balloon.
Riding in the balloons he was measuring radiation in the atmosphere.
He was looking for the source of ionizing radiation that registered on an electroscope.
At the time, the prevailing theory was that the radiation came from rocks. To test that theory, in 1909 German scientist Theodor Wulf measured the rate of ionization near the top of the Eiffel tower (at a height of about 300 metres) using a portable electroscope.
Though he expected the ionization rate to decrease with height, Wulf noted that the ionization rate at the top was just under half that at ground level – a much less significant decrease than anticipated.
In 1911 Victor Hess conduducted his first balloon borne experiment, reaching an altitude of about 1100m.
Hess found "no essential change" in the amount of radiation compared with ground level.
Then, on 7 August 1912, in the last of seven flights that year, Hess made an ascent to 5300m.
There he found the rate of ionization was some three times that at sea level and concluded that penetrating radiation was entering the atmosphere from above.
In an earlier flight he had found no noticeable drop during a partial solar eclipse, so he could rule out the Sun as the source.
What will be the main motivation for humanity's future space endeavours?Related story: (See story)
The cost of losing nature