Sea level cosmic ray intensity and threshold rigidity

The intensity of the nucleon component has been measured with a shipboard neutron monitor during a number of voyages between Oct. 1956 and March 1959. After reduction and normalization the intensity has been plotted as a function of the rigidity value computed by Quenby and Wenk. Four limited regions excepted, the point distribution is confined to a comparatively narrow band corresponding to the errors of measurement. Corrected threshold values are given for the regions in which the points fall outside the general distribution. These regions are all inside the geomagnetic latitudes between which Quenby and Wenk had to interpolate for the penumbral effect.