Various properties of the new group of low energy primary cosmic-ray particles ($E<\mathrm{}1.6\mathrm{}$ Bev for protons) which enter the top of the atmosphere at geomagnetic latitudes north of 52° were investigated during the summer of 1950. Measurements at both 52°N (Swarthmore, Pennsylvania) and 69°N (Fort Churchill, Manitoba) were obtained with the same quadruple-coincidence counter trains used previously, oriented either horizontally or vertically, and with pulsed ionization chambers biased to detect bursts exceeding 1.0 $\mathrm{P}\mathrm{o}-\alpha$.

No diurnal or temporal variations in the cosmic-ray intensity were detected, and no change between 1949 and 1950 was indicated.

Flights were conducted with counter trains containing various thicknesses of interposed Pb absorber.

In contrast with the 46 percent increase in the vertical intensity between the two stations, no latitude effect was revealed either in the flux of cosmic rays traveling in the horizontal direction or in the frequency of bursts detected by the ionization chambers, at the highest altitudes attained (∼9 mm of Hg).

The data permit conclusions to be drawn regarding the horizontal component, the solar dipole-moment, the nature of the low energy spectrum, as well as nuclear disintegrations and primary heavy nuclei.

• Received 14 December 1951

DOI:https://doi.org/10.1103/PhysRev.86.536