Aërial Navigation A Popular Treatise on the Growth of Air Craft and on Aëronautical Meteorology

The purpose of this work is to portray in popular terms the substantial progress of aëronautics from its earliest beginning to the present time. Beyond the introductory account, little note is taken of experiments, however picturesque or clever, which constitute no advance in the art, or lead to no useful result. At times some minutiæ are presented to complete the story of an important series of achievements; but the unproductive efforts of impractical zealots, however prominent or widely known in their day, receive scant, if any, attention. Failures and tragedies where introduced, are described for the lessons involved rather than for any curious interest investing them. The griefs and grotesque follies of aëronautic imbeciles form a long story, but a futile and unprofitable one, of slight concern in the evolutionary history of a veritable science.

A general history of aërial locomotion would naturally be divided into four parts, treating respectively of passive balloons, power balloons, passive flyers, and power flyers; but in this work a separate treatment has not been allotted to passive flyers because of their too backward state of development. Passive gliders which maneuver in the air merely by virtue of gravitational force, or acquired momentum, are familiar enough; but the much more interesting passive flyers of human construction, adapted to rise without motive power considerably beyond their initial level, or to soar far aloft, and sail long distances by virtue of favorable winds, are still in their infancy. It may be hoped, however, that the vulture’s art which now is well nigh overlooked, because of the triumphant advance of dynamic flight, will soon receive such attention that future treatises may relate human achievements in soaring that shall rival the dexterous and marvelous feats of the condor and albatross, even as the majestic sweep of the dynamic aëroplane now rivals the powerful rowing flight of the strongest birds of prey.

Following the story of the evolution of air ships, a brief account of the medium they navigate has been added. In particular, the circumstances which affect the density and motion of the air have been studied; for the density of the air determines the static lift of air ships; the density and speed of impact of the air together determine the dynamic lift and the resistance to progression; while the velocity of the air current conditions the possible speed of travel in any direction. It is important, therefore, that the aëronautical student should have some acquaintance with the general properties of the air which affect its density, and some knowledge of the generation and prevalence both of the great currents of the atmosphere, and of the local winds and invisible turmoils which so nearly concern the safety and effective progress of the aërial navigator.

The French units of measurement have been freely used, as well as the English. This seems advisable because the official rules and records of international aëronautic events are partly expressed in the metric system. Moreover, the navigation of a universal medium seems to call for such universal standards. Indeed a peculiar mission of world travel is to eliminate provincialism, and to promote universalism of thought, of sentiment, and of custom.

In order to lighten the book for the popular reader, some interesting historical facts and much important quantitative data are placed in the Appendices, where they may be available to the technical or special student.

It is a pleasant duty to acknowledge here my obligations to the U. S. Signal Corps, the Smithsonian Institution, and the U. S. Weather Bureau, for much assistance in collecting the materials for this work. Dr. W. J. Humphreys, of the U. S. Weather Bureau, has very kindly read the manuscript for the chapters on the atmosphere.

My thanks are due also to the Scientific American and to Aëronautics for the use of photographs for the illustrations, as also to the manufacturers of various aircraft, and to Mr. W. J. Hammer, Mr. Carl Dientsbach, and Mr. A. S. Levino.

A. F. ZAHM.

COSMOS CLUB WASHINGTON, D. C., January, 1911.