It will easily be understood that 1,200 furnaces were not too many to melt these 60,000 tons of iron simultaneously.  Each of these furnaces contained about 1,400,000 lbs. of metal; they had been built on the model of those used for the casting of the Rodman gun; they were trapezoidal in form, with a high elliptical arch.  The warming apparatus and the chimney were placed at the two extremities of the furnace, so that it was equally heated throughout.  These furnaces, built of fireproof brick, were filled with coal-grates and a “sole” for the bars of iron; this sole, inclosed at an angle of 25 deg., allowed the metal to flow into the receiving-troughs; from thence 1,200 converging trenches carried it down to the central well.

The day following that upon which the works of masonry and casting were terminated, Barbicane set to work upon the interior mould; his object now was to raise in the centre of the well, with a coincident axis, a cylinder 900 feet high and nine in diameter, to exactly fill up the space reserved for the bore of the Columbiad.  This cylinder was made of a mixture of clay and sand, with the addition of hay and straw.  The space left between the mould and the masonry was to be filled with the molten metal, which would thus make the sides of the cannon six feet thick.

This cylinder, in order to have its equilibrium maintained, had to be consolidated with iron bands and fixed at intervals by means of cross-clamps fastened into the stone lining; after the casting these clamps would be lost in the block of metal, which would not be the worse for them.

This operation was completed on the 8th of July, and the casting was fixed for the 10th.

“The casting will be a fine ceremony,” said J.T.  Maston to his friend Barbicane.

“Undoubtedly,” answered Barbicane, “but it will not be a public one!”

“What! you will not open the doors of the inclosure to all comers?”

“Certainly not; the casting of the Columbiad is a delicate, not to say a dangerous, operation, and I prefer that it should be done with closed doors.  When the projectile is discharged you may have a public ceremony if you like, but till then, no!”

The president was right; the operation might be attended with unforeseen danger, which a large concourse of spectators would prevent being averted.  It was necessary to preserve complete freedom of movement.  No one was admitted into the inclosure except a delegation of members of the Gun Club who made the voyage to Tampa Town.  Among them was the brisk Bilsby, Tom Hunter, Colonel Blomsberry, Major Elphinstone, General Morgan, and tutti quanti, to whom the casting of the Columbiad was a personal business.  J.T.  Maston constituted himself their cicerone; he did not excuse them any detail; he led them about everywhere, through the magazines, workshops, amongst the machines, and he forced them to visit the 1,200 furnaces one after the other.  At the end of the 1,200th visit they were rather sick of it.