"You will observe," said the major, "that by describing an arc, with Paris as the center of the circle, and a radius of about seventy-five miles, you will include a small sector of the German trenches. Roughly speaking this arc will extend from about Hamegicourt to Conde, both within the German lines, I am sorry to say. Now then, somewhere in this arc, or perhaps back of it, the German gun is placed. Anywhere else where it would be possible for such a monster engine of war to be erected, would bring it too close to our batteries.

"So that gives us the comparative location of the gun," went on the French officer. "But the next question is not so easy to settle--how to get rid of it. As I said, I think we shall have to depend on you airmen."

"Well, we're for the job!" exclaimed Tom.

"I know you are. And it may fall to you, or to your friends. I will talk of that later."

"Have you been able to get any idea of the kind of gun it is, or why it fires at fifteen minute intervals?" asked Jack.

"We have been able to get no really reliable information save that which we deduce by our observations of this sh.e.l.l and from what we know of the location of our own and the German lines," the Major went on. "Up to now our airmen have not been able to penetrate far enough without being attacked, and such few as did get well over toward the Rhine could make out nothing. I have no doubt the gun is well camouflaged."

"And is it true that it doesn't fire at night because the Germans are afraid the flashes will be seen?" asked Tom.

"That may have been the reason at first, but they have fired at night, of late, so they must have some way of concealing the flashes, or perhaps setting off other flashes at the same time so as to confuse our scouts."

"It's going to be some job," murmured Jack.

"You said something," agreed his chum.

They remained talking a little longer, and some of the officers who knew the reason for Tom's visit to Paris, expressed regret that he had no information as yet about his father.

"But take heart," one told him. "He is not dead, or we should have heard of it. Of course he may have fallen into the hands of the Germans, and then we would not know for some time."

"He may have been caught," agreed Tom. "While Tuessig is out of the game on account of his injuries, he may be able to direct Potzfeldt, and that scoundrel would have good reason for trying to get revenge on us."

"Ah, yes, I heard about your rescue of the young lady and her mother,"

said the major. "It was a brave deed."

"Oh, any one could have done it," said Tom, modestly.

"And have you seen them since they came to Paris?" the major proceeded.

"No, but I wish we could find them!" burst out Jack, and then he blushed at his impetuosity, while Tom murmured something about "Bessie," and Jack promptly told him to hold his tongue.

"Perhaps you may meet them sooner than you expect," went on the French officer.

"Now I wonder what he could have meant by that?" asked Jack, as he and his chum went out, after a final look at the German sh.e.l.l. "Does he know where they are?"

"It wouldn't be surprising, seeing that Mrs. Gleason is probably in Red Cross work, and Bessie may be helping her. We should have looked them up before," went on Tom. "But what with searching for my father, and the excitement about the bombardment, I really forgot all about them."

Jack did not say whether he had or not, the chances being that he had, more than once, thought of Bessie Gleason.

During the next two days the monster cannon continued to shoot sh.e.l.ls at intervals into Paris. Some did considerable damage, as any sh.e.l.l would do in a great city, and many unfortunates were killed. But there was no reign of terror such as, undoubtedly, the Boches hoped to create. Paris remained calm, and there were even jokes made about the cannon. It was called a "Bertha" and other names, the former referring to Bertha Krupp, one of the owners of the great German ordnance works.

Word was given out that the French gunners on the front were trying to reach the big gun with their missiles. But as they were firing blindly it could not be said what havoc had been wrought.

"But, sooner or later, we'll get the range, and get within striking distance," said one of the French officers. "Then we'll show them a trick or two."

"Have the aviators done anything toward trying to find the gun?" asked Tom. "I mean anything more."

"We are perfecting our plans for the flying corps," was the answer.

"Perhaps you shall know more in a few days."

"Well, I hope we'll be here when the fun begins," said Tom, grimly.

"We've got another extension of leave, and I'm going to ask the police now, to co-operate with the military in seeking my father."

"I think that will be a wise plan. We will give you all the help we can."

But the quest for Mr. Raymond seemed a hopeless one, and as no confirmation could be had of his death or injury, the idea gradually became fixed in the minds of Tom and Jack that he had been made a German prisoner.

"If that is so, and I can get any trace of him, I'll go over the Rhine to get him back," snapped Tom.

"And I'll go with you!" declared his chum.

It was a few days after they had inspected the German "dud," and the boys were wondering what new developments might take place, the sh.e.l.ling of Paris meanwhile continuing at intervals, that one evening the boys were visited in their lodgings by Major de Trouville.

"Is there any news?" eagerly asked Tom, for he guessed that the French officer would not be paying a merely social call. Those were the strenuous days when such things had pa.s.sed.

"Well, yes, news of a sort," was the answer. "But what I came to find out was whether you were so taken with these lodgings that you could not be induced to move."

"To move!" exclaimed Jack.

"Yes. Have you found anything unhealthful here?"

"Why, no," replied Tom, wonderingly. "We like it here. The landlord couldn't be nicer, and we're in a good location."

"Nevertheless, I fear I shall have to ask you to change your quarters,"

went on the major, and by the quizzical smile on his face the boys guessed that there was something in the wind.

"Let me ask you another question," went on the French officer. "Have you been annoyed since you have been here?"

"Annoyed? How?" inquired Tom.

"By unwelcome visitors, or by strangers."

The boys thought for a moment.

"There's one chap who lives in the same building here, whom we've seen on our staircase several times," said Jack, slowly. "Once I saw him pause at our door with a key, as though he were going to enter, but he heard me coming, and, muttering that he had taken too much wine and was a bit hazy in his memory, he went on upstairs."

"I thought as much," the major said. "Was the man you speak of familiar to you?"

"No, I can't say that he was," replied Jack, and Tom nodded his acquiescence. "I never saw him before."

"Oh, yes you have," and the major smiled.

"I have? Where?"

"On the train, coming into Paris."