CHAPTER XV. THE AEROPLANE IN THE GREAT WAR Balloon Observations. Changed Conditions in Warfare. The Effort to Conceal Combatants. Smokeless Powder. Inventions to Attack Aerial Craft. Functions of the Aeroplane in War. Bomb-throwing Tests. Method for Determining the Movement of a Bomb. The Great Extent of Modern Battle Lines. The Aeroplane Detecting the Movements of Armies. The Effective Height for Scouting. Sizes of Objects at Great Distances. Some Daring Feats in War. The German Taube. How Aeroplanes Report Observations. Signal Flags. How Used. Casualties Due to Bombs From Aeroplanes. GLOSSARY INTRODUCTORY In preparing this volume on Flying Machines the aim has been to present the subject in such a manner as will appeal to boys, or beginners, in this field of human activity. The art of aviation is in a most primitive state. So many curious theories have been brought out that, while they furnish food for thought, do not, in any way, advance or improve the structure of the machine itself, nor are they of any service in teaching the novice how to fly. The author considers it of far more importance to teach right principles, and correct reasoning than to furnish complete diagrams of the details of a machine. The former teach the art, whereas the latter merely point out the mechanical arrangements, independently of the reasons for making the structures in that particular way. Relating the history of an art, while it may be interesting reading, does not even lay the foundations of a knowledge of the subject, hence that field has been left to others. The boy is naturally inquisitive, and he is interested in knowing WHY certain things are necessary, and the reasons for making structures in particular ways. That is the void into which these pages are placed. The author knows from practical experience, while experimenting with and building aeroplanes, how eagerly every boy inquires into details. They want the reasons for things. One such instance is related to evidence this spirit of inquiry. Some boys were discussing the curved plane structure. One of them ventured the opinion that birds' wings were concaved on the lower side. "But," retorted another, "why are birds' wings hollowed?" This was going back to first principles at one leap. It was not satisfying enough to know that man was copying nature. It was more important to know why nature originated that type of formation, because, it is obvious, that if such structures are universal in the kingdom of flying creatures, there must be some underlying principle which accounted for it. It is not the aim of the book to teach the art of flying, but rather to show how and why the present machines fly. The making and the using are separate and independent functions, and of the two the more important is the knowledge how to make a correct machine.