All this racket was lost upon the two so far above the earth. They heard nothing of the bleat of the firing guns. Even the bursting of shrapnel went unheeded, save at a time when a shell exploded close by, and was faintly heard.
Tom was wisely taking but little chance. He maintained an altitude that prevented most of the shrapnel from coming anywhere near the plane.
They crossed the enemy front, and sped on. The bombardment diminished in fury as they left the first and second line trenches behind them. It was continued to some extent from an elevation further back, but as Tom knew of this formation, and had crept up still higher, no accident happened to them.
At last the air service boys were fully launched on their night voyage through the upper currents. Tom waited until he considered that it was really safe to change their course. He did not want to betray his movements in case some daring Boche pilot started up in a swift Fokker machine to pursue them.
Once he shut off the engines and volplaned down a thousand feet or more. This was done because it was intensely cold up where they were; and the reasons that had kept them at such a high altitude existed no longer. Then again Tom wished to listen to discover if there was another aircraft near them; and this could be done only when his motor was silent.
"No pursuit, Jack!" he managed to call to his chum before they once more straightened out, and again allowed the motor to send forth its loud hum.
Jack had no chance to make any sort of reply. It did not matter, for he, too, had eagerly listened, and had failed to catch any telltale sound.
Immediately Tom shaped a new course. No longer were they heading toward the north by east, but directly east. There some forty miles, more or less, away, lay the city of Metz, the object of their mission.
After moving along in this fashion for a short time Tom drove his machine more slowly. He was watching for the rising of the old moon ahead, where the horizon was already lighted with her near approach.
How strange she looked peering above the edge of the world as though curious to see all that was going on in this troubled hemisphere. Jack thought he had never witnessed a more peculiar spectacle. But at least this fragment of a moon would be likely to afford them the necessary illumination required when they attempted to land in a field that neither of them had ever seen before, and only knew through information imparted by means of their chart, and its accompanying notes.