But Roque and Renos kept constant vigil with glasses, and Billy wondered that the pair did not get a crick in the neck with all the head-turning they did.
A sharp order advised the pilots to send the biplanes farther aloft, and circle. The French fortress of Belfort could be seen directly underneath.
The aviators well knew that an explosion close to an aëroplane is often sufficient, through the force of the air concussion alone, to bring it down, and they knew they could not chance a close shot from the long-range guns in the fort.
Though the machines now evoluted at greater height, the powerful glasses enabled the observers to plainly distinguish the movements below.
It was quickly manifested that the garrison lookout had become aware of the aërial visitation, and that they did not approve of the color of the hovering aircraft.
A couple of smokeballs ascended and burst in the center of a cloudrack far to the right of the machine. Renos broke his record for silence with a shrill cackle.
"Save your powder, you numbskulls," he shouted for his own satisfaction.
Roque seemed oblivious of the gunplay below. As the biplane described great circles over the fort, he kept his glasses steadily aimed at a point in the enclosure over which the flag was floating.
The men who emerged from the officers' quarters all wore the French uniform.