# Air Service Boys over the Rhine/Chapter 20

CHAPTER XX
THE BIG GUN
For a moment Tom and Jack did not quite know what to make of the excitement of Major de Trouville. And excited he certainly was beyond a doubt.
"You must come and tell this to Lieutenant Laigney at once," he said. "It may mean something important. Are you sure of the sequence of the colors?" he asked. "That makes all the difference."
"There was first an orange tint," said Tom, "which was followed by green and purple, the last gradually dying out."
"Orange, green and purple," murmured the major. "Can it be that for which we are seeking?"
He hurried along with the boys, seemingly forgetting, in his haste and excitement, that he was their ranking officer. But, as has been noted, the aviators are more like friends and equals than officers and men. There is discipline, of course, but there is none of the rigidity seen in other branches of the army. In ​fact the very nature of the work makes for comradeship.
Tom and Jack knew, slightly, the officer to whom Major de Trouville referred. Lieutenant Laigney was an ordnance expert, and the inventor of a certain explosive just beginning to be used in the French shells. It was simple, but very powerful.
"You must tell him what you observed—the strange colored lights, my boys," said the major. "By the way, I hope you carefully noted the time of the colored flares."
Tom and Jack had. That was part of their training, to keep a note of extraordinary happenings and the time. Often seemingly slight matters have an important bearing on the future.
They found Lieutenant Laigney in his quarters, making what seemed to be some intricate calculations. He saluted the major and nodded to the boys, whom he had met before.
'"Lieutenant," began Major de Trouville, "these young gentlemen have something to tell you. I want you to think it over in the light of what you told me about the action of that new explosive you said the Germans might possibly be using."
"Very good. Major. I shall be delighted to be of any service in my power," was the answer.
​Then Tom and Jack described what they had seen, giving the location of the colored lights as nearly as they could, and the exact time they had noted them.
"How long would it take a shell to reach Paris, fired at a distance of eighty miles from the city?" asked the major.
The lieutenant made some calculations, and announced the result of his findings.
"Then," went on the commanding officer, "if a shell was fired from the big gun, say at the moment when these two scouts observed the tri-colored fire, it should have reached Paris at seven-fifty-three o'clock."
"As nearly as can be calculated, not knowing the exact speed of the projectile, yes," answered the lieutenant.
Major de Trouville picked up the telephone and asked to be connected with the wireless station.
"Have you had any reports of the bombarding of Paris this evening?" he asked. "Yes? What time did the first, or any particular shell, arrive? Ah, yes, thank you. That is all at present."
He turned to the others, after having listened to the reply and put the instrument away.
"One of the shells exploded in a Paris street at seven-fifty-two o'clock this evening," he said. ​"It beat your calculations by one minute, Lieutenant Laigney."
"Ah! Then this means—" and the younger officer seemed as excited as the major had been when Tom and Jack told him what they had seen.
"It means," finished the commanding officer, "that, in all likelihood, these young men have discovered the location of the big German cannon."
"Discovered it!" cried Jack. "Why we didn't see anything!"
"Nothing but those queer lights," added Tom.
Major de Trouville smiled at them, and Lieutenant Laigney nodded his head in assent.
"Those queer lights, as you call them," said the ordnance expert, "were the flashes of a new explosive. What the Germans call it I do not know. For want of a better name we call it Barlite, from the name of Professor Barcello, one of our experimenters, who discovered it. But a spy stole the secret and gave it to Germany. They must have managed to perfect it, though we have not used it as yet, owing to the difficulty in constructing a gun strong enough to withstand its terrific power."
"And do you mean they're using this explosive in the big German gun?" asked Jack.
​"And that we really saw it being fired?" cried Tom.
"That is my belief," said the lieutenant. "This explosive burns, when fired from a gun, first with an orange flame, changing to green and then to purple, as the various gases are given off."
"Those are the very colors we saw!" exclaimed Jack.
"Yes," went on Major de Trouville. "And when I heard you mention them, and when I recalled that Lieutenant Laigney had spoken of a certain explosive that gave off a tri-colored light, I suspected you had hit on the German secret."
"And do you believe we actually saw the giant cannon being fired at Paris?" asked Tom.
"Without a doubt. The time of the arrival of one of the shells coincides almost to the minute with the time that would elapse after the missile was sent on its way, and this was when you saw the queer flashes. You have discovered the area where the big gun is placed. All that is needed now are some exact observations to give us the exact spot."
"And then we can destroy it!" cried the lieutenant. "Then the menace to beloved Paris will have passed!"
"And thanks to our brave American friends!" ​cried the major, shaking hands with Tom and Jack. "You will win promotion for this!" he murmured.
"But the big gun isn't found yet," said Jack.
"Why, if you are right, sir," Tom said to the major, "the shells must pass right over our camp."
"They probably do. But at so far above—several miles up so as to reach the height of thirty-five—that we never know it. We neither see them nor hear them. Boys, I believe you have located the big gun! All that now remains is to destroy it!"