A swallow, one of the very best flyers, lifts itself with difficulty from the ground. An eagle, particularly after eating, has to run some distance flapping its wings vigorously before it can rise. An insect, possessing considerable spring-power in its limbs, always takes a good jump at the moment its wings are spread out for elevation, at an upward angle forward. With similar contrivances for the purpose must a practical flying machine be provided. It should, in combination with a certain amount of spring power, to enable it to rise with greater ease at the final moment, and also to reduce the shock in alighting to a minimum, have wheels to run over the ground, until sufficient force and momentum has been attained to launch it into the boundless realms of space. To be thoroughly practical, the machine must be under perfect control, and be made to descend upon any spot desired with absolute safety and ease. This can be accomplished by the combined effort of the propellors and wings. By exerting the power of these contrivances in opposite directions the disturbed atmosphere is thrown in volumes underneath the machine, which, on account of its similarity to a parachute, although of a greatly different form, can be made to descend vertically and very slow. The doubt expressed by many, that the guidance of an air ship is possible, is easily refuted. All bodies, possessing the propelling force within them, can guide themselves in an elastic medium. Of this we have millions of examples before us in all flying creatures. Finally, a practical shape and proper size and weight will form one of the most essential elements in a successful flying machine, and which has been disregarded more or less so far. Of course, it is impossible to calculate already, before an actual machine has been built and datas can be fixed, the limits of these factors in the average ærial structure. My impressions are, that the weight of a single carriage will be from 400 to 500 lbs., inclusive; a motive force of 3 to 5 horse power. It will have a total length of from forty to fifty feet, by about the same in width, from tip to tip; and a surface of from 500 to 600 square feet will be more than sufficient to sustain a total weight of 1000 lbs.; for such a machine will be capable to carry from three to four persons, or its equivalent weight of express matter, letters, newspapers, and other light freight. Of course, free mail facilities for our wise solons will, perhaps, unfortunately have to be barred out.