Two smoke trails and the refractive images of shock fronts seen against a charge support tower, in the same experiment. The time at which this picture was taken is the same as for the previous picture, but the two pictures were taken on diametrically opposite sides of the explosion. Above, from the top down and counter-clockwise: the primary shock front, the reflected shock front, the contact surface, also seen as a kink in the smoke trails, and the Mach stem shock front. The triple point, where the three shocks meet, is in the centre of the picture.