Immediately after the Rome conference, Rossi carried out two experiments that led to a significant advance in the understanding of cosmic rays. Both involved triple coincidences of pulses from three Geiger counters; but in the first, the counters were aligned and separated by blocks of lead, while in the second, they were placed in a triangular configuration such that all three could not be traversed by a single particle travelling in a straight line. Results from the first configuration demonstrated the existence of cosmic-ray particles capable of penetrating 1 metre (3 ft 3 in) of lead.