It was the 22nd of November.  The supreme departure was to take place ten days later.  One operation still remained to bring it to a happy termination, a delicate and perilous operation exacting infinite precautions, and against the success of which Captain Nicholl had laid his third bet.  It was, in fact, nothing less than the loading of the gun and the introduction into it of 400,000 lbs. of gun-cotton.  Nicholl had thought, not without reason, perhaps, that the handling of so large a quantity of pyroxyle would cause grave catastrophes, and that in any case this eminently explosive mass would ignite of itself under the pressure of the projectile.

There were also grave dangers increased by the carelessness of the Americans, who, during the Federal war, used to load their cannon cigar in mouth.  But Barbicane had set his heart on succeeding, and did not mean to founder in port; he therefore chose his best workmen, made them work under his superintendence, and by dint of prudence and precautions he managed to put all the chances of success on his side.

First he took care not to bring all his charge at once to the inclosure of Stony Hill.  He had it brought little by little carefully packed in sealed cases.  The 400,000 lbs. of pyroxyle had been divided into packets of 500 lbs., which made 800 large cartridges made carefully by the cleverest artisans of Pensacola.  Each case contained ten, and they arrived one after the other by the railroad of Tampa Town; by that means there were never more than 500 lbs. of pyroxyle at once in the inclosure.  As soon as it arrived each case was unloaded by workmen walking barefoot, and each cartridge transported to the orifice of the Columbiad, into which they lowered them by means of cranes worked by the men.  Every steam-engine had been excluded, and the least fires extinguished for two miles round.  Even in November it was necessary to preserve this gun-cotton from the ardour of the sun.  So they worked at night by light produced in a vacuum by means of Ruehmkorff’s apparatus, which threw an artificial brightness into the depths of the Columbiad.  There the cartridges were arranged with the utmost regularity, fastened together by a wire destined to communicate the electric spark to them all simultaneously.

In fact, it was by means of electricity that fire was to be set to this mass of gun-cotton.  All these single wires, surrounded by isolating material, were rolled into a single one at a narrow hole pierced at the height the projectile was to be placed; there they crossed the thick metal wall and came up to the surface by one of the vent-holes in the masonry made on purpose.  Once arrived at the summit of Stony Hill, the wire supported on poles for a distance of two miles met a powerful pile of Bunsen passing through a non-conducting apparatus.  It would, therefore, be enough to press with the finger the knob of the apparatus for the electric current to be at once established, and to set fire to the 400,000 lbs. of gun-cotton.  It is hardly necessary to say that this was only to be done at the last moment.