Abstract
The mean free path of charged particles that produce penetrating showers has been measured in carbon, sulfur, and iron. Preliminary measurements with carbon were carried out at 130-m elevation and the mean free path obtained was 89±12 g/cm2. Measurements at 2765-m elevation gave mean free paths in carbon, sulfur, and iron of 65±5, 76±7, and 115±12 g/cm2, respectively. The carbon data were used to get an estimate of the mean free path in nuclear matter of high energy nucleons.