She explained that the screws were made of a metal called aluminum, rare then, because so difficult to extract from its combining substances, and almost useless on account of its being impossible to weld. Her father, however, had found a way to utilize it--how, she did not know. If this ascension proved a success the French government would receive the balloon and the secret of the steering and propelling gear, along with the formula for the silvery dust used to inflate it. Even she understood what a terrible engine of war such an aërial ship might be, from which two men could blow up fortress after fortress and city after city when and where they chose. Armies could be annihilated, granite and steel would be as tinder before a bomb or torpedo of picric acid dropped from the clouds.
On the 10th of August, a little after five o'clock, Jack left Lorraine on the terrace at Morteyn to try once more to see the marquis--for Lorraine's sake.
He turned to the west, where the last Uhlan of the rear-guard was disappearing over the brow of the hill, brandishing his pennoned lance-tip in the late rays of the low-hanging sun.
"Good-by," he said, smiling up at her from the steps. "Don't worry, please don't. Remember your father is well, and is working for France."
He spoke of the marquis as her father; he always should as long as she lived. He said, too, that the marquis was labouring for France. So he was; but France would never see the terrible war engine, nor know the secrets of its management, as long as Napoleon III. was struggling to keep his family in the high places of France.
"Good-by," he said again. "I shall be back by sundown."
Lorraine leaned over the terrace, looking down at him with blue, fathomless eyes.
"By sundown?"
"Yes."
"Truly?"
"Yes."
"Tiens ta Foy."
"Always, Lorraine."
She did not chide him; she longed to call him Jack, but it stuck in her white throat when she tried.
"If you do not come back by sundown, then I shall know you cannot," she said.
"But I shall."
"Yes, I believe it."
"Come after me if I don't return," he laughed, as he descended the steps.
"I shall, if you break your faith," she smiled.
She watched him out of sight--he was going on foot this time--then the trees hid him, and she turned back into the house, where Madame de Morteyn was preparing to close the Château for the winter and return to Paris.
It was the old vicomte who had decided; he had stayed and faced the music as long as there was any to face--Prussian music, too. But now the Prussians had passed on towards Metz--towards Paris, also, perhaps, and he wished to be there; it was too sad in the autumn of Lorraine.