For the separation of low energy mesotrons from the electrons a block of lead 1.25 cm thick was placed above a pair of anticounters such that any electron which generates a shower in it is removed by the anticounters. An additional block of lead was also placed below the anticounters to absorb any electron which escaped the system without producing a shower in the upper lead piece. The mesotrons thus separated from the electrons were examined in a Wilson chamber having a 2-cm block of lead across the center. 937 single tracks were observed to traverse the 2-cm lead block and all these tracks were ascribed to mesotrons. There was a case of a shower of three particles found to be generated in the lead piece inside the chamber and this shower was attributed to a knock-on process. It was also found out that the additional lead block whose thickness was to be 4 cm, according to Bhabha, could be reduced to 2 cm at sea level without disturbing the efficiency of the system. By an experiment with counters it was also found out that 1.25 cm of lead corresponds to the maximum for showers of two or more particles initiated only by electrons in lead. © 1948 The American Physical Society.