"But I saw a Voisin at one of the hangars which had a big gun on it," said Ralph.
"Ah, that was the Voisin Cannon, which carries a 37-millimetre gun," said the lieutenant. "That is used for bombarding captive balloons and Zeppelins, if the latter should ever make their appearance."
"A 37-millimetre gun?" repeated Alfred.
"Yes; that's about one and a half inch in your measure," answered the lieutenant.
Within an hour the reservoir was again in position, and there was no delay in again mounting into the air. "We might take a little trip due east, as far as Toul, and north of that point we may have the privilege of seeing some of the enemy," remarked the lieutenant, as they mounted the machine.
A beautiful silver thread now appeared on the landscape to the east, as they reached their greatest altitude. Looking back there was a smaller thread to the west, and, apparently, the same distance from their viewpoint. They thus had the opportunity of seeing, at one glance, two of the most noted rivers which figure in the great war,—the Meuse to the east, and the Marne in the west, these streams at this point being within thirty miles of each other.
It was, probably, imprudent for them to take an out-of-the-way course to reach their destination, but the temptation was very great. The sun was still shining brightly when they started from Ligny-en-Barrois, but it was now growing dark from the overspreading clouds, and as soon as Toul was sighted the lieutenant turned the machine northward.
To the west it could now be seen that the threatening clouds were coming up, and they appeared to be sweeping toward the east with great speed, at right angles to the aviators' course.
"I wonder what the lieutenant will do?" queried Ralph half to himself, as he looked at the clouds, and then glanced back to the officer.
The lieutenant shook his head, and pointed the machine further to the left.