Complex sentence: The capacitance of the glass couples the trigger pulse into the envelope where it exceeds the breakdown voltage of gas surrounding one or both of the electrodes, forming spark streamers, which propagate via capacitance along the glass at a speed of 1 centimeter in 60 nanoseconds.
Split into simpler sentences: The capacitance of the glass couples the trigger pulse into the envelope where it exceeds the breakdown voltage of gas surrounding one or both of the electrodes, forming spark streamers. The streamers propagate via capacitance along the glass at a speed of 1 centimeter in 60 nanoseconds.