In two high-altitude rocket flights of thin-walled Geiger tubes at geomagnetic latitudes 64\ifmmode^\circ\else\textdegree\fi{} and 74\ifmmode^\circ\else\textdegree\fi{}N, a considerable intensity of soft radiation has been encountered above 50 kilometers altitude. No such radiation has been found in flights of identical equipment at 88.5\ifmmode^\circ\else\textdegree\fi{} and at 55.6\ifmmode^\circ\else\textdegree\fi{}. The radiation is tentatively interpreted as the high-energy tail of the auroral spectrum. It may consist of electrons.

The total charged particle cosmic-ray intensity above the atmosphere has been measured with thin-walled Geiger counters (total effective stopping power of apparatus and residual atmosphere 0.5 g/${\mathrm{cm}}^{2}$ of aluminum) carried in balloon-launched rockets at geomagnetic latitudes 54.3\ifmmode^\circ\else\textdegree\fi{} N, 62.1\ifmmode^\circ\else\textdegree\fi{} N, 71.9\ifmmode^\circ\else\textdegree\fi{} N, and 86.7\ifmmode^\circ\else\textdegree\fi{} N. The respective values of unidirectional particle intensity averaged over the upper hemisphere are: $\overline{J}=0.44\ifmmode\pm\else\textpm\fi{}0.01, \ensuremath{\le}0.50\ifmmode\pm\else\textpm\fi{}0.05, \ensuremath{\le}0.50\ifmmode\pm\else\textpm\fi{}0.05, \mathrm{and} =0.48\ifmmode\pm\else\textpm\fi{}0.01$ ${({\mathrm{cm}}^{2}\phantom{\rule{0ex}{0ex}}\mathrm{s}\mathrm{e}\mathrm{c}\phantom{\rule{0ex}{0ex}}\mathrm{s}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{a}\mathrm{d})}^{\ensuremath{-}1}$. These results are consistent with the complete or nearly complete absence of primary cosmic rays having a magnetic rigidity less than 1.7\ifmmode\times\else\texttimes\fi{}${10}^{9}$ volts.

Measurements of the intensity of heavy primary cosmic-ray nuclei have been made above the atmosphere by means of the new Iowa balloon-launched rocket ("rockoon") technique at geomagnetic latitudes $\ensuremath{\lambda}=56\ifmmode^\circ\else\textdegree\fi{}, 76\ifmmode^\circ\else\textdegree\fi{}, \mathrm{and} 86\ifmmode^\circ\else\textdegree\fi{}$. The measuring instrument was a thin-walled, pulse-ionization chamber of 15-cm diameter. The observed data, in conjunction with geomagnetic theory, demonstrate a complete or nearly complete absence of primary heavy nuclei of $Z\ensuremath{\ge}6$ having a magnetic rigidity less than 1.5\ifmmode\times\else\texttimes\fi{}${10}^{9}$ volts ($\frac{p}{\mathrm{mc}}<0.8$), the result being the most significant for the C, N, O group. It is noted that this spectral cutoff occurs at closely the same magnetic rigidity, and distinctly not at the same velocity, as the previously reported cutoff in the spectra of primary protons and $\ensuremath{\alpha}$ particles.

A large multiplate counter controlled cloud chamber containing 300 g/${\mathrm{cm}}^{2}$ of gold has been used for the study of penetrating showers at an altitude of 11,500 ft. The minimum energy required to trip the counter control efficiently was about 15 Bev. Counters located inside the chamber made it possible to observe events initiated by both ionizing and non-ionizing particles. It was found that at least 83.5 percent of the particles initiating these high energy events were ionizing. From the distribution of events in the plates of the chamber, the mean free path in gold for the particles producing these penetrating showers was found to be 145\ifmmode\pm\else\textpm\fi{}15 g/${\mathrm{cm}}^{2}$. The projected zenith angle distribution of the shower primaries could be approximately represented by ${cos}^{m}\ensuremath{\theta}$, where $m$ was in the range 8 to 10. Since the measurements were made at 680 g/${\mathrm{cm}}^{2}$ atmospheric depth, this corresponds to an absorption mean free path in air of 70 to 90 g/${\mathrm{cm}}^{2}$. The flux of particles capable of producing these high energy showers was found to be (1.7\ifmmode\pm\else\textpm\fi{}1) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}6}$ particles ${\mathrm{cm}}^{\ensuremath{-}2}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ ${\mathrm{sterad}}^{\ensuremath{-}1}$. This value, when compared with the flux of the primary protons at the top of the atmosphere, yielded an absorption mean free path of 71\ifmmode\pm\else\textpm\fi{}5 g/${\mathrm{cm}}^{2}$. Application of the Gross transformation changed this value to 77\ifmmode\pm\else\textpm\fi{}5 g/${\mathrm{cm}}^{2}$. The large mass of the gold nucleus plus the presence of two mean free paths of material inside the chamber made it very unlikely that only a small fraction of the energy of the primary particles be lost in the cloud chamber.