sets forth with clearness the problem as it stands to-day. When it is fully solved--and it certainly seems solvable--right and left steering will be a less difficult matter, and alighting will be accomplished by killing the momentum when near the ground by an abrupt upward slant of the main aeroplanes; but this is an anticipation and a digression. Now to return to the instrument we are considering: this soaring machine is intended to gain velocity by a swoop, and then automatically steer itself into a horizontal or very slightly descending course, as indicated by B and C in Fig. 2. It depends upon the principle that the pendulum rod always seeks the perpendicular; for instance, when the machine is launched pointing steeply downward, the positions of the pendulum and aeroplanes are as shown in Fig. 5; therefore the steering aeroplane C will, as soon as velocity is gained, lay a strong hold upon the wind of flight, and have a tendency to bring the machine into a horizontal course. Now, if the length of the rod MM is made correct by adjustment at the pivot-holes near N, when the desired course, a very gentle decline, is reached, both aeroplanes will be approximately horizontal, as shown in Fig. 6. If, however, the machine deviates either upward or downward from its intended course, the weight at the end of the pendulum causes the steering aeroplane to correct the error. Fig. 7 shows the effect of a slight upward deviation. [Illustration: _FIG. 5 ---- FIG. 6 ---- FIG. 7_] H represents a long and very slender air-receptacle made of thin rubber and inflated; this should be pointed at both ends. It may be used to keep the machine afloat when experiments are made near the water. I have not yet used this, but have allowed my machines to go to pieces. The design here given calls for aero_planes_ as being more easily made than aero_curves_ modelled after the wings of birds, but in all probability the latter will eventually displace the former. * * * * * We are brought now, after this consideration of the greatest mechanical problem of the age, to ask, What shall be done to bring to our own century the credit and honor of reaching the solution? The answer is, encourage experiments with soaring machines. Have regattas and large prizes. Appeal to the people’s love of sport, and show what possibilities of recreation have been suggested by the experiments of Otto Lilienthal. Tobogganing on ice we can have only a few weeks in the year: tobogganing on air is possible at all seasons. When we have made our aeroplanes or aerocurves automatic in their steering action, flights like Lilienthal’s will be, to say the least, no more dangerous than football and quite as interesting.