he 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 o