Popular Science Monthly 



531 



the vast improvements that have been made 

 in motors. Without this enormous techni- 

 cal advance men could not fly with im- 

 punity close to the ground. As the writer 

 prophesied many years ago, the direct 

 result of. this progress is the creation of 

 what may be 

 termed "a 

 second zone 

 of safety." 

 The first 

 zone lies 

 high in the 

 air, far be- 

 y ond the 

 range of 

 anti-aircraft 

 guns. Let 

 the aircraft 

 drop close 

 to the earth, 

 let it all but 

 graze church 

 spires, and 

 it enters this 

 second zone 

 of safety — a 

 zone which 

 becomes 

 safe because 

 of the 

 breathless 

 speed with 

 which the 

 pilot flies. 

 Why did 

 cavalry pa- 

 trols, in the 

 old days, 

 ride up boldly upoh the enemy? Well do 

 I remember how we were surprised in a 

 sham battle in 1892 by the sudden ap- 

 pearance of three "enemy" hussars who 

 craned their necks over a ridge not sixty 

 yards away. Our captain finally managed 

 to blurt out: "Well, somebody shoot at 

 them." But they were gone long before 

 we could reach the stacked rifles. What is 

 .the twenty-miles-an-hour that a cavalry 

 horse can do compared with the ninety- 

 miles an hour expected even of slow flying 

 machines today? Who can hope to hit the 

 small one-hundred-and-thirty-mile-an-hour 

 fighter as he flits over the ground ? 



As soon as the airplane developed its full 

 power of flying near the ground as well as 

 high up in the azure, it became a real bird of 

 prey, fighting in the only efficient way that 

 a bird can fieht. which means at close 



Hundreds of captive balloons are used by each of the armies. 

 Artillery officers watch the effect of gunfire from their baskets. 

 Airplanes attack the balloons and drop bombs upon them. 

 The balloons go up in smoke, while the officers descend 



range. This development is simply the 

 automatic outcome of the perfected art of 

 fighting with airplanes — likewise efficient 

 only at close range. After an air-man feels 

 certain of himself, it is second nature to 

 apply the same methods close to the ground 



— just as the 

 falcon fights 

 a weasel. 

 And so the 

 "second 

 zone of 

 safe-ty," 

 near the 

 ground, was 

 quite inci- 

 dentally dis- 

 covered. 



Alpine 

 hunters 

 must learn 

 how to fight 

 enraged 

 eagles. The 

 troops in the 

 trenches 

 must con- 

 tend with 

 machine gun 

 bullets com- 

 i n g from 

 above. Now 

 do you see 

 why that 

 photograph 

 is an his- 

 toric docu- 

 ment? 



Let Cheese Be Your Principal 

 Meat Substitute 



A POUND of cheese supplies more than 

 twice as much energy as a pound of 

 fowl or round steak and almost twice as 

 much protein as the same amount of fowl or 

 ham. It is, pound for pound, more 

 nourishing than any meat. Why, there- 

 fore, do we not use it as a substitute for 

 meat? 



According to the Department of Agri- 

 culture we do not appreciate the value of 

 cheese as a food ; we think it is indigestible. 

 Yet more than ninety per cent of the pro- 

 tein of cheese is digested and ninety per 

 cent of its energy is available. For this one 

 reason alone it should form an important 

 part of the daily fare. When cooked it is as 

 easilv digested as any other article of diet. 



