Summary

This monograph presents the experimental evidence and theoretical considerations supporting Victor Hess's groundbreaking discovery of cosmic rays. Hess's central thesis is that ionizing radiation of extraterrestrial origin penetrates the Earth's atmosphere from above, a phenomenon he meticulously documented through high-altitude balloon ascents. He quantitatively measured increasing radiation levels with altitude, demonstrating that atmospheric absorption alone could not account for the observed intensity. The work details the experimental setup, the atmospheric conditions during the ascents, and the crucial observations made at altitudes exceeding 5,000 meters.

Hess concludes that a new, penetrating radiation exists, originating from outside the Earth. The book details the measurements of ionization rates in different atmospheric layers, providing the foundational data for the subsequent identification and study of cosmic rays. Readers gain an understanding of the experimental rigor and observational data that led to the postulation of this ubiquitous and energetic radiation.

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Key concepts

Ionization — The process of an atom or molecule acquiring a negative or positive charge by gaining or losing electrons, respectively.
Gamma Rays (γ-Strahlen) — High-energy electromagnetic radiation, which Hess initially posited as the source of the penetrating radiation.
Altitude Dependence of Radiation — The observed increase in ionizing radiation intensity as altitude increases, indicating an external source.
Balloon Ascents — High-altitude flights using balloons to carry instruments for atmospheric measurements.