contemplated superposed aeroplanes of very great length from port to starboard. The size in the other direction was more for the purpose of preventing a rapid fall than for a lifting effect. I saw that it would be necessary to have horizontal fore and aft rudders placed a long distance apart, so as to prevent rapid pitching, and it appeared to me that the further these rudders were apart, the easier it would be to manœuvre the machine. As I never had any doubts regarding the efficiency of screw propellers working in the air, I decided to use two of these of a large size rotating in opposite directions. Of course, all this speculation was theory only, but I verified it later on by actual experiments before I built my machine, and it is very gratifying to me to know that all the successful flying machines of to-day are built on the lines which I had thought out at that time, and found to be the best. All have superposed aeroplanes of great length from port to starboard, all have fore and aft horizontal rudders, and all are driven with screw propellers. The change from my model is only a change in the framework made possible by dispensing with the boiler, water tank, and steam engine. In this little work, I have dealt at considerable length with air currents, the flight of birds, and the behaviour of kites, perhaps at the expense of some repetitions; as the resemblance between kite flying and the soaring of birds is similar in many respects, repetitions are necessary. To those who go to sea in ships, it is necessary to know something of the currents they are liable to encounter; if it be a sailing ship, certainly a knowledge of the air currents is of the greatest importance, and so it is with flying machines. If flights of any considerable distance are to be made, the machine is liable at any time to encounter very erratic air currents, and it has been my aim in discussing these three subjects--air currents, birds, and kites--to bring them before the would-be navigators of the air, in order that they may anticipate the difficulties they have to deal with and be ready to combat them. Then, again, there has been almost an infinite amount of discussion regarding the soaring of birds and the flying of kites. Many years ago, after reading numerous works on the subject of flight, I became a close observer myself, and always sought in my travels to learn as much as possible. I have attempted to discuss this subject in simple and easily understood language, and to present sufficient evidence to prevent the necessity of any further disputes. I do not regard what I have said as a theory, but simply as a plain statement of absolute and easily demonstrated facts. During the last few years, a considerable number of text-books and scientific treatises have been written on the subject of artificial flight, the most elaborate and by far the most reliable of these being the “Pocket-Book of Aeronautics,” by Herman W. L. Moedebeck, Major und