310 SCIENCE OF HOME AND COMMUNITY 



to the army. During this war airplanes have served an 

 important purpose as scouts, to examine the enemies' re- 

 doubts, to take photographs, to detect movements of soldiers, 

 and to direct the artillery fire. 



Several distinct types of airplanes have been devised for 

 war purposes, such as the scouting plane, the fighting plane, 

 and the bombing plane. The crew of a scouting plane con- 

 sists of a pilot and observer. It can travel at great speed 

 and was used to report movements of the- enemy, to take 

 photographs, and to direct artillery fire by means of the 

 wireless outfit with which it is provided. The fighting plane 

 carried one person and was built to climb quickly and fly 

 faster than any other type of plane. (See figure 125.) This 

 was equipped with a machine gun which could be fired 

 straight ahead, between the propeller blades, without hitting 

 them. The bombing planes have been well called the dread- 

 naughts of the air. (See figure 126.) They are large and 

 powerful and so constructed that they can carry between 

 one and two tons of explosives. These were used to drop 

 bombs on vital portions of the enemies' lines such as supply 

 depots and railway junctions. 



During this war such tremendous strides have been made in 

 the art of flying there seems little doubt that flying machines 

 and airships will soon be common throughout the civilized 

 world, and will be used for commercial purposes to transport 

 passengers and cargoes. Doubtless more rapid develop- 

 ment in air navigation was made during the four years of 

 war than would have been made in fifteen or twenty years in 

 peace times. 



How the airplane is kept up. Having traced the develop- 

 ment of the airplane from its crude beginnings to its present 

 perfected state, we may next inquire how it is constructed 

 and on what principle it works. The balloon is kept up 

 because the gas which it contains is lighter than air; but 

 the airplane is heavier than air and is kept up by a different 



