Cosmic rays. A rain of energetic photons, protons & other atomic nuclei reaches Earth from space. These primary cosmic rays collide with atoms in the atmosphere to give showers of other particles: protons (p), neutrons (n), light nuclei (N), neutrinos (v), pions (pi) & muons (mu). Muons and neutrinos can reach far underground. Cosmic ray research began when Wulf went up the Eiffel Tower. Hess proved their cosmic origin. Cosmic rays were observed on the Pic du Midi in France & Pikes Peak in the US. Kolhorster reached 9000m & unmanned balloons 30, 000m. Today cosmic rays are detected undergound at Super-Kamiokande in Japan and underwater by Antares in the Mediterranean.