Before the outbreak of the war there were many military engines awaiting a practical trial in actual service, among them the dirigible balloon. During a period of forty years the nations of the world have been obliged to do a good deal of guessing, in spite of calculations based on previous experience in wars whose mechanism was very simple and crude as compared with the present engines of war. But the improvements in weapons employed on terra firma did not constitute so far a step away from experience as engines of aërial warfare. Those engines of war which have been mainly the subjects of guess-work are the aëroplane and that dreadnought of the air, the Zeppelin, especially the latter. The advent of the aëroplane introduced an entirely new set of problems. Before the advent of the aëroplane, the navigation of the air was confined to the balloon. Contrary to expectation, the aëroplane, instead of putting the balloon out of the race, served only to stimulate higher development of the balloon, with the result that the dirigible balloon and the aëroplane have been developed side by side. From the outset, it was recognized that the chief desideratum in the development of the aëroplane consisted in greater stability, and especially in automatic equilibration. The first aëroplanes were very imperfect. At the time of the early exhibitions which I witnessed, it was necessary to plan them to take place in the calm of the evening, just before sundown. The aëroplane could not go up in a wind. No aëronaut would have undertaken to go up except when there was no wind. Even a moderate breeze made them quite unmanageable. Now, however, the aëroplane can rise in a gale of wind, and fly right into the teeth of a hurricane. The old-style balloon could only go with the wind. It could make no headway against it, but had to float like a feather on the lightest breeze. The modern dirigible, however, which has reached its highest degree of perfection in the Zeppelin, can travel through still air at a speed of sixty miles an hour, the speed of a gale of wind, and can brave a fifty-mile gale at a speed of ten miles an hour. This is altogether remarkable when we take into account the fact that the Zeppelin, with all its load, must be lighter than air, and therefore, for its size, lighter than the fluffiest eiderdown. LIMITATIONS OF THE AËRIAL BOMB Aviation makes a strong appeal to the imagination, and this fact, together with errors and misconceptions in the popular mind concerning the use and power of high explosives, has led to many strange predictions and weird conclusions about the destruction which dirigibles and aëroplanes would be capable of doing by dropping bombs from the sky.