Note by E G Richardson, on a paper 'Supersonic dispersion in gases II. Air containing water vapour' by M Mokhtar and E G Richardson Sectional Committee: Physics Certifies that the paper 'contains no information of use to the enemy in the prosecution of the war; it does not contravene the Official Secrets Act'. [Published in the 'Proceedings of the Royal Society of London'] No received date. November 1939