Among the experimenters listed in ‘A Directory of Heavier-Than-Air Flying Machines in Western Europe, 850 BC-AD 1783’, was the name of Charles Bernouin, a surgeon of Grenoble, who was said to have flown from a high tower in Regensburg on 15 January 1673. A colleague in Germany has recently sent me two broadsheets, published soon after the event, which show that Bernouin, who has often been mentioned in histories of aviation, should be removed and placed in the ‘List of Rejected Items.’

Flows around two-dimensional rectangular cavities driven by thick shear layers are investigated experimentally at two supersonic Mach numbers (Me = 1.5 and 2.5) to show the effects of variations in Mach number and length to depth ratio of the cavity. Flow oscillation is observed in the cavity. The characteristics of the oscillatory behaviour are determined by Mach number and the length of depth ratio of the cavity, as well as the shear layer spanning the cavity. Two oscillatory mechanisms can be identified: one in which a strong trailing-edge vortex and vortices which are shed from the leading-edge interact, the other in which a transverse oscillation of a single vortex occurs within the cavity. Changes in the time-dependent and the time-mean flow characteristics at different flow conditions are discussed.

The time-dependent experimental results are compared with existing theoretical analyses of the frequencies. For one of these characteristic types of oscillation, the longitudinal oscillation, an existing theoretical description is improved with a modified phase relation.