Frederick William Lanchester, Aerodynamics, constituting the first volume of a complete work on aerial flight… (1906)
“ The condition of equilibrium is that the resultant of the two forces passes through the pivot centre E. It is evident that these two forces, in equilibrium at any one speed, will be in equilibrium for all speeds, for their relative direction undergoes no change, and they are each proportional to the velocity squared and so are proportional to one another. The bob weight D is made adjustable on the arm D and the condition of equilibrium is ascertained by trial. ”
