"On receiving the baton, steam was again turned on, and the train passed on to the bridge... when the train had got about 200 yards from the cabin [in the signal box], he observed sparks flying from the wheels; and after they had continued about three minutes, there was a sudden bright flash of light, and in an instant there was total darkness, the tail lamps of the train, the sparks, and flash of light, all, he said disappearing at the same instant."
2021 November 3, Dr Joseph Brennan, “Boxes with functions across the centuries”, in RAIL, number 943, page 57, referring to the Tay Bridge disaster