"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!"
