It cannot fail to be a subject for remark that in spite of the very large amount of work which has been done in this country on the subject of formal stability calculations, these calculations do not form a part of routine design of the majority of aircraft firms, nor are they used by the Air Ministry as a standard process of checking the aerodynamical qualities of an aeroplane. I use the term “ formal ” stability calculations to cover the solutions of the equations of motion of an aeroplane in rectilinear flight developed from Bryan's work.