Short reaction time Geiger counters have been used at sea level to study the time coherence of associated cosmic ray particles under 18cm of Pb, and also in air. A 50-channel hodoscope has been used to identify the events giving coincidences between two 138 cm2 trays of these counters separated by 15 cm in a horizontal plane. No evidence was found for delays between associated particles of the order of 2 × 10-8 sec, as reported by Robinson using spark counters, although the counter resolving time of 1.4 × 10-8 sec should have allowed detection of the effect. Multiple hits by particles on the Geiger counter trays were found to give modified counter reaction time distributions, and it is suggested that a similar effect could occur in spark counters. A theory which accounts for the behaviour of both spark and Geiger counters under multiple hit conditions has been developed.