About three o'clock the signals between the repellers became very frequent, and soon afterwards a truce-boat went out from Repeller No. 1. This was rowed with great rapidity, but it was obliged to go much farther up the harbour than on previous occasions, in order to deliver its message to an officer of the garrison.
This was to the effect that the evacuation of the fort had been observed from the Syndicate's vessels, and although it had been apparently complete, one of the scientific corps, with a powerful glass, had discovered a man in one of the outer redoubts, whose presence there was probably unknown to the officers of the garrison. It was, therefore, earnestly urged that this man be instantly removed; and in order that this might be done, the discharge of the motor-bomb would be postponed half an hour.
The officer received this message, and was disposed to look upon it as a new trick; but as no time was to be lost, he sent a corporal's guard to the fort, and there discovered an Irish sergeant by the name of Kilsey, who had sworn an oath that if every other man in the fort ran away like a lot of addle-pated sheep, he would not run with them; he would stand to his post to the last, and when the couple of ships outside had got through bombarding the stout walls of the fort, the world would see that there was at least one British soldier who was not afraid of a bomb, be it little or big. Therefore he had managed to elude observation, and to remain behind.
The sergeant was so hot-headed in his determination to stand by the fort, that it required violence to remove him; and it was not until twenty minutes past four that the Syndicate observers perceived that he had been taken to the hill behind which the garrison was encamped.
As it had been decided that Repeller No. 2 should discharge the next instantaneous motor-bomb, there was an anxious desire on the part of the operators on that vessel that in this, their first experience, they might do their duty as well as their comrades on board the other repeller had done theirs. The most accurate observations, the most careful calculations, were made and re-made, the point to be aimed at being about the centre of the fort.
The motor-bomb had been in the cannon for nearly an hour, and everything had long been ready, when at precisely thirty minutes past four o'clock the signal to discharge came from the Director-in-chief; and in four seconds afterwards the index on the scale indicated that the gun was in the proper position, and the button was touched.
The motor-bomb was set to act the instant it should touch any portion of the fort, and the effect was different from that of the other bombs. There was a quick, hard shock, but it was all in the air. Thousands of panes of glass in the city and in houses for miles around were cracked or broken, birds fell dead or stunned upon the ground, and people on elevations at considerable distances felt as if they had received a blow; but there was no trembling of the ground.
As to the fort, it had entirely disappeared, its particles having been instantaneously removed to a great distance in every direction, falling over such a vast expanse of land and water that their descent was unobservable.
In the place where the fortress had stood there was a wide tract of bare earth, which looked as if it had been scraped into a staring dead level of gravel and clay. The instantaneous motor-bomb had been arranged to act almost horizontally.
Few persons, except those who from a distance had been watching the fort with glasses, understood what had happened; but every one in the city and surrounding country was conscious that something had happened of a most startling kind, and that it was over in the same instant in which they had perceived it. Everywhere there was the noise of falling window-glass. There were those who asserted that for an instant they had heard in the distance a grinding crash; and there were others who were quite sure that they had noticed what might be called a flash of darkness, as if something had, with almost unappreciable quickness, passed between them and the sun.