Ilford Nuclear Research photographic plates have been exposed at the Jungfraujoch, altitude 3,457 metres, under lead screens of various thicknesses up to 28 cm. The intensity of the stars, and its variation with the number of tracks forming them, have been recorded for each thickness of absorber. The absorption curve of the star intensity shows that the range in lead of the radiation causing the stars is 310±20 gm/cm². The size distribution is apparently the same under all absorbers.The intensity and size distribution have also been recorded in similar plates exposed at sea level. The size distribution is again the same as that found for the high altitude plates, but the range in air of the primaries is 150±7 gm/cm².These results are consistent with the generally accepted view that the majority of the stars is caused by neutrons.