= Hess cosmic-ray balloon experiment
{c}
<Victor Franz Hess>'s 1912 series used two sealed, 3-mm-walled <ionization chambers> with <Theodor Wulf>'s fiber <electrometers>. <Karl Bergwitz> suggested internal plating; Günther & Tegetmeyer improved focusing. Basket-mounted ground comparisons, insulation-loss measurements, simultaneous detectors and barograph-derived heights supplied checks. The highest flight reached 5350 m; its comparisons came from Vienna and after landing, without a launch-site baseline.<Über Beobachtungen der durchdringenden Strahlung bei sieben Freiballonfahrten by Victor Franz Hess>[1912, pp.1084-1085 apparatus and preparations; pp.1087-1088 seventh flight; English primary-text translation https://arxiv.org/pdf/1808.02927 pp.1-2, 5-6]{ref}
A third, thin-walled chamber admitted ambient air. Hess multiplied its readings by $750/b$, with <pressure> $b$ in millimeters of mercury, warning that vessel-wall contributions might violate this scaling. He recorded outside <temperature> but applied no absolute-temperature correction. Night flights, an eclipse and weather observations constrained alternatives to radiation from above; the eclipse argument addressed directly propagating solar radiation.<Über Beobachtungen der durchdringenden Strahlung bei sieben Freiballonfahrten by Victor Franz Hess>[1912, p.1085 pressure reduction; p.1086 eclipse; p.1088 temperature footnote; pp.1090-1091 inference; English translation pp.2-3, 6-8]{ref}
The <electrometers> read gradual <electric potential> loss caused by continuing air <ionization>. The low-altitude dip and strong high-altitude rise favored an extraterrestrial contribution, without measuring <proton> composition.<Über Beobachtungen der durchdringenden Strahlung bei sieben Freiballonfahrten by Victor Franz Hess>[1912, pp.1089-1091 altitude averages and interpretation; English translation pp.7-8]{ref} An <ionization chamber> integrates <electric charge>: one energetic particle may create many <ion pairs>, several particles may contribute to one reading, and a <photon> can create <charged particles> in the gas or walls. A voltage-loss reading is therefore neither a count of <primary cosmic rays> nor a chemical analysis of them.
<Domenico Pacini> supplied independent evidence: in June 1911 he compared a copper-box-enclosed <electroscope> at the sea surface and 3 m underwater, more than 300 m offshore above an 8-m-deep seabed. Reduced underwater <ionization>, stable electrical loss between runs, and a lake comparison supported an external contribution independent of soil <radioactive decay>. Water provided shielding; this established a different constraint from Hess's altitude comparison.<La radiazione penetrante alla superficie ed in seno alle acque by Domenico Pacini>[Pacini's 1912 report, English translation pp.3-5, especially surface/underwater comparison and residual-ionization discussion; original Italian facsimile pp.9-14]{ref}
\Image[/hess-ionization-chamber-readout.png]
{title=From air ionization to electrometer discharge}
{description=Original functional schematic and invented readout example for the <ionization-chamber charge-loss model>. The chamber drawing is not a dimensional reconstruction, and the plotted voltage traces are not Hess's measurements.}
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