This paper is intended as a sequel to “Stability in Aviation” and deals with* Problem 2 in Chapter XI. (p. 178). The long list of problems there given will show that before the book was written or even commenced, investigations had been projected and contemplated more than sufficient to fill a second volume on the Rigid Dynamics of Aeroplane Motions, my book on stability constituting the fiist. It will be found that the necessity of mathematical investigation in connection with stability, and other aeroplane problems was first mentioned by me in “Science Progress” for October, 1897, and it would have been a great advantageif the completion of most of this work had preceded the first aeroplane flights. With reasonable facilities and assistance, longitudinal stability could have been completed by about ,1900, lateral by 1904; the unwritten second volume would have been in the printers’ hands by January, 1910.