The optical phenomena occurring during the initiation of breakdown in the trigatron spark gap in air have been investigated with voltages up to 1 MV and inter-electrode spacings up to 60 cm, using an image converter as an electro-optical shutter. Measurements of gap current flowing during the breakdown initiation process have also been made. The optical phenomena are similar in nature to those occurring in long untriggered gaps. One or more leader strokes occur, followed by a main stroke. Leader stroke velocities fall within the range 5 × 10⁶ to 3.2 × 10⁸ cm sec^-1, depending on experimental conditions. The average mainstroke velocity is about 10⁸ to 10⁹ cm sec^-1. Under certain conditions the path taken by the complete spark is partly governed by the production of a short leader stroke originating at one electrode. It is shown that this leader occurs only in the region of the gap where conditions laid down by Loeb and Meek and Raether as being suitable for streamer formation and propagation are satisfied.