Did Hess believe cosmic rays were dangerous?
A common misconception is that I considered cosmic rays harmful. In fact, my early work focused on their physical properties, not biological effects. I measured their ionization and penetrating power, finding them to be extremely energetic but low in intensity at sea level. Later in my career, I did study their biological effects, particularly after my emigration to the United States in 1938. In my 1949 book 'Cosmic Radiation and Its Biological Effects,' I collaborated with biologists to examine potential impacts on living organisms. However, I always emphasized that the natural background cosmic radiation at Earth's surface is too weak to pose significant risk to humans. The real danger comes from artificial sources or prolonged exposure at high altitudes, such as for airline crews. My position was always grounded in measurement: let us measure, and then we shall know. The data show that cosmic rays are a fascinating natural phenomenon, not a health hazard under normal conditions.
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