Little was said about the manner of manipulating the double rudder and torsional wings; for the rules of manipulation would vary in different machines, depending upon structural design and external conditions. For example, if the proposed fin and vertical rudder were ample and suitably placed, the lateral balance could be controlled by merely twisting the wings, without touching the vertical rudder; but if the fin and rudder were not adequate, the lateral poise would be controlled by twisting the wings and working the vertical rudder conjunctively. A novice might prefer leaving the rudders fixed and controlling the poise in short flights by twisting the wings by means of a single lever having two independent movements, one to rotate the wings oppositely, the other to rotate them identically. The principle of control expressed in italics had been set forth also in a preceding paragraph. Having proposed means for securing both stability and steadiness about each of the three axes of an aëroplane, the text continued: “These ends could probably be attained very well by mounting two compound aëroplanes on a long backbone,[36] somewhat after the manner of the Hargrave cellular kites, and adding a compound rudder to the whole.” ... “_If the inclination of the sustainers, front and back, could be altered independently, it might be feasible for a pilot to preserve the equilibrium of the machine even when its center of gravity was frequently shifted, as by the moving of passengers to and fro._”[37] At that date, 1893, an inventor doubtless could have secured a broad claim on a mechanism embodying the torsion-wing-and-double-rudder mechanism of control. But in those days aviation was pursued largely as a liberal study by scientific men who wished to hasten the advent of practical flight, by presenting important physical measurements and principles which could be freely employed by all. Accordingly the three-rudder system of control seems not to have been claimed by an inventor much before the close of the nineteenth century. Since then it has been patented in one form or other by many practical aviators, some endeavoring to claim the whole broad contrivance, others claiming more restricted devices.