The reason that Barbicane & Co. had chosen the country of the Wamasai as the scene of their operations was that, in the first place, it was little known and rarely visited by travellers, and, secondly, that the mass of Kilimanjaro offered all the qualities of solidity and position necessary for their work. Besides, the country was rich in all the materials they required, and these were found under conditions that made them easily workable.
A few months before leaving the United States, Barbicane had learnt from the Swedish explorer that iron and coal were abundant in the Kilimanjaro chain. There were no mines to be opened, and no shafts to be driven thousands of feet into the crust of the earth. The minerals were on the surface, and had only to be picked up from the ground. And in addition to these, there were large deposits of nitrate of soda and iron pyrites, such as were required for the manufacture of the meli-melonite.
Barbicane and Nicholl had brought no staff of workmen with them except the ten foremen, on whom they could depend. These could take command of the ten thousand negroes placed at their disposal by Bali-Bali, to whom was entrusted the task of making the monster cannon and its no less monster projectile.
A fortnight after the arrival of Barbicane and his colleague among the Wamasai, three large workshops had been erected on the south of the mountain; one as the foundry for the gun, one as the foundry for the shot, and one as the factory for the meli-melonite.
And how did Barbicane & Co. intend to cast a cannon of such colossal dimensions? The only chance for the inhabitants of the world was, as we have seen, in the difficulty of dealing with such a huge undertaking.
To cast a cannon a million times larger than a four hundred pounder would have been beyond the power of man. To make a four hundred pounder is difficult enough, but a four hundred million pounder! Barbicane and Co. did not attempt to do so. It was not a cannon, nor even a mortar, that they had in their minds. They simply intended to drive a gallery into the mountain.
Evidently this enormous mine would have the same effect as a gigantic Columbiad, the manufacture of which would have been as costly as it was difficult, owing to the thickness it would have to be to avoid the risk of bursting. Barbicane & Co. had always intended to act in this way, and if J. T. Maston’s note-book spoke of a cannon, it was the four hundred pounder he had taken as the basis of his calculations.
Consequently, a spot was chosen a hundred feet up the southern side of the chain, from the base of which the plains extended for miles and miles, so that nothing would be in the way of the projectile when it was hurled from the long tube in the mass of Kilimanjaro.
With great precision and much labour Barbicane carried on the driving of his tunnel. Easy to him was the construction of boring machines worked with air compressed by the power of the large waterfalls in the district. The holes bored by the machines were charged with meli-melonite, and the blasting of the rock was easy, it being a kind of syenite composed of orthoclastic felspar and amphibolic hornblende. It was a favourable circumstance that a rock so constituted would strongly resist the frightful pressure developed by the expansion of the gas; but the height and thickness of the mountain afforded ample security against any exterior splitting or cracking.
The thousands of workmen under the guidance of the ten foremen, superintended by Barbicane, progressed with such zeal and intelligence that in less than six months the tunnel was finished. It measured nearly ninety feet in diameter and two thousand feet long. As it was important that the projectile should glide along a perfectly smooth surface without losing any of the gas of deflagration, the interior was lined with a smooth tube of cast iron. This was a much larger affair than the celebrated Columbiad of Tampa Town, which had sent the aluminium projectile round the Moon. But what is there that is impossible to the engineers of the modern world?