Abstract
IN his Symons Memorial Lecture delivered before the Royal Meteorological Society on March 15, Mr. P. M. S. Blackett dealt with “Cosmic Radiation”. The study of what is now known as cosmic or penetrating radiation began more than thirty years ago with the experimental investigation of the conductivity of the air in closed vessels. By 1932, measurements of the ionisation had been carried out up to heights of 28 km. in the atmosphere and down to depths of 230 m. under water. The ionisation is found to be 100,000 times more intense at the highest point reached compared with that at the greatest depth. More than four hundred papers have been written on the subject and still the nature of the primary radiation is not certain and its origin quite unknown. The ionisation is constant in time to within two per cent at any one place, but is about twelve per cent less intense at the equator than in latitudes of 50° N. and S. From these latitudes to the poles it is nearly constant. It is probable, but not certain, that the primary radiation incident on the earth's atmosphere consists of an isotropic corpuscular radiation with a mean energy of more than 1010 volts. The actual ionisation at sea level is due to fast particles, mainly electrons, protons and ‘positive electrons’. The tracks of these particles can be photographed by the cloud method and such photographs have shown that very complex pheno mena of great variety and interest occur in connexion with the absorption of the primary cosmic rays by matter.
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Cosmic Radiation. Nature 131, 429 (1933). https://doi.org/10.1038/131429c0
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DOI: https://doi.org/10.1038/131429c0