The velocity of the spread of discharge due to photons in 100% filled Bromine Geiger Muller Counter with three separate and divided cathodes has been determined by measuring the time in a waveform monitor taken by the discharge from the first to the third counter. Propagation velocity of discharge in a Br2counter was compared with that of an argon and alcohol mixture counter. The velocity of spread of discharge in the former lies between 0.32 × 108and 0.92 × 108cm/sec for Br2at a pressure of 10 cm Hg and in the latter, varies between 1.1 × 107and 2.7 × 107cm/sec.