AERIAL NAVIGATION.*
WE have hardly yet recovered from the astonishment caused by the results of the Rheims Aviation Meeting. Only the other day it was counted a marvel if a man propelled himself through the air for the fraction of a minute ; then we woke up one morning to find that a man had flown across the Channel. Now he can fly as long as there is any fuel for his engines. It has taken three-quarters of a century to perfect the railway engine and the steamship on a surface and in a medium which we profess to know something about, but aero- planes seem to have been born like midges on a summer evening. Moreover, many of the laws that govern aerial navigation are to be easily comprehended by the common man, and Mr. Turner puts them so lucidly and attractively that one is a little anxious lest Dick or Harry should insist on gliding from the attic window or the leads instead of descending by the staircase or the banisters: The apparatus which would give most people the clearest notion of the use of the planes of a flying-machine is the box-kite of Hargreave. If the observer can once fully understand that it keeps its position and stability because the several surfaces resist the air at different angles, and thus correct each other, he has begun the grounding of his education.
No doubt the even more important laws of the " stream- line " form, the concavo-convex form of plane, and the pro- portion of the width of the plane to its length will be under- stood too. It has been discovered that this form, which is possessed by most fishes, offers the least resistance to the air. That is to say, an egg driven through the air blunt end fore- most offers less resistance than if driven with the pointed end foremost. This law governs the lines of a yacht, and it has been embodied in the planes of flying-machines, which are not flat but curved, and also have their entering edge—i.e., the front edge—blunt and growing thicker and then tapering away. Any one can realise the practicability of this form by taking the wings of a bird. Which is the thickest part ? The front with the rounded surface. So the military dirigibles of the Continent are built like a slender pear for the same reason. The chapter explaining these truths leaves little to be desired, and cannot fail to excite the interest and wonder of all, for it at once unfolds a mechanical law of great beauty and simplifies the construction of aeroplanes. The members of a flying-machine must conform to the same rule, and a concavo-convex section enables the planes to be constructed hollow, ensuring the same strength with lightness.
It is with some difficulty that we leave the fascinating subject of the aeroplane to draw attention to the scarcely less important chapters on the condition of the atmosphere. Aeronauts have discovered the air to be a much more complex medium to fly in than it appears to be from the ground. The contour of the earth's surface means all sorts of dis- turbing currents, and the calmest atmosphere is never so still as one thinks it is; so that "aviators" prefer to manceuvre over a plain for excellent reasons. One truth is undeniable : that the "aviator" will have to face cold as well as wind in high flights. Other points which this really fascinating book emphasises are the necessity of would-be "aviators" going through a probation of gliding, the unsolved problem of the bird's power of gliding, and the caution that motorists are not "aviators" and mechanical flight not merely a question of motors. As regards the dirigible balloon, the aeronaut has still the problem of the contraction and expansion of gas to contend with, and any man who advances the solution of these and other problems will deserve well of the country.
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