"Now, boys," said the sergeant, addressing the special squad delegated for the building of the chapparal, "plant several of the heavy poles with the brushy tops on each side of the gun; then stretch wires across and hang the small brush to them. Be sure to distribute them irregularly, so as to make it as natural as possible." Shovels and picks were now employed feverishly to dig the holes and plant the poles. The wires were strung and the decorations added, not only along and around the location of each gun, but in the spaces between the pieces. The vans came up continually with new burdens of boughs, until the boys thought there would be no end to this new species of arbor culture. "Ralph, do you think we could spot this place at a distance of five thousand feet in a swift Morane?" asked Alfred. "I should say not," replied Ralph, "but there is one thing I should do if I had anything to say about it." "And what is that?" asked the captain, who overheard the remark. "I'd completely cover the breech of the gun and the ammunition case," he answered. "And why?" asked the captain, with a smile. "Because the merest glimpse of shiny metal is likely to be noticed when flying. I have seen that many times when flying, and Lieutenant Guyon always told us to watch for it," replied Ralph. "You are right," answered the captain. "That will be your work. Here, men, follow the instruction of these boys as to the placing of the boughs." The sergeant showed his pleasure at the order, for he somehow felt himself to be sponsor for the boys. "You've got the old man going," he whispered to the boys. "Shall I go to the next gun?" inquired Alfred, addressing the captain. "By all means; orderly, instruct the workers to follow the direction of the young men," said the captain. CHAPTER IV A LESSON IN OBSERVATION The strenuous work was completed before night covered the scene. The flying machines had acted as a screen, and the guns, now in position, were effectually covered from the eyes of a prying foe. As they were about to leave the captain said: "For the present you may find room in the vans, but tomorrow the regular quarters will be prepared near the guns." The steaming hot supper, which was brought up in the kitchen vans, was relished as never before. After the meal they sat around and talked over the incidents of the day, and learned each other's histories, for there is a comradeship in the field that obtains nowhere else in any other occupation. "And so you have been flying?" said the sergeant. "That has always had a fascination for me, but, strange as it may seem, I have never yet been up in the air, although I have had many opportunities. I have often wondered how things look from a height of two kilometers." "Well, the first time I went up I couldn't distinguish a thing," said Ralph. "I could tell what trees were, and could make out rivers, and houses, of course, but outside of that everything else looked like a blurred picture."