Meanwhile Ehrenbreitstein and Coblentz continued under bombardment from the Frenchmen. The enemy's fire-pots never failed to find the grand-duke's quarters, notwithstanding the fact that he changed them every day. This at last became so annoying that treason began to be suspected, and the duke offered a reward for the detection of the spy who gave the information to the enemy. That a spy was at work in the German camp was beyond question, though the outlets of both cities were so closely guarded that it would have been impossible for a living mortal to pass through them. Nor could the treason have been committed by means of carrier-pigeons, for, whatever of domestic fowl-kind had been in the cities had long since been devoured by the hungry citizens. The mayor, ever on the alert for transgressors, had his suspicions as to who might be the spy. Every man but one in the beleaguered cities fasted, lamented, prayed, cursed, wept, as the case might be, save this one man, who remained constantly cheerful, smiling, well-fed.
When one of the Frenchmen's fiery monsters came hissing and spitting into the fortress this one man, instead of taking to his heels and seeking the shelter of a cellar, as did the rest of his comrades, would coolly wait until the fire-pot fell to the ground, and, if it failed to burst he would dig it out of the earth into which it had bored itself and carry it to the foundry.
Surely this was more than foolhardiness!
The constable always opened the enemy's unexploded fire-pots in his subterranean work-room; refilled them there, then hurled them back without delay. There was something more than amusement behind this.
One day, when Hugo came up from his subterranean workroom, he encountered the mayor, who said to him:
"Stay, constable, I want to see what you put into that fire-pot—open it."
Without a moment's hesitation Hugo unscrewed the lid and revealed the explosives wrapped in coarse linen; at the same time he explained how much gunpowder, hazel-wood charcoal, sulphur, resin, pitch, sal-ammoniac, borax and acetate of lead were necessary to make up the amount of unquenchable fire required for the bomb.
"Very good," quoth the city functionary, "but what beside these is there in the bottom of the pot?"
"Under this earthen plate, your honor, is more gunpowder. When the explosives on top are burnt out this plate, which has become red-hot, explodes the powder and bursts the bomb—that is the whole secret of the infernal machine."
"I should like to see what is under the earthen plate."