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? While the boring went on in the flank of Kilimanjaro, the workmen were busy at the second foundry. While the tube was being built the enormous projectile was in process of manufacture. All it consisted of was a mass of cast iron, cylindro-conical in form, weighing one hundred and eighty thousand tons. It had never been intended to make such a casting in one piece, but to provide one hundred and eighty masses, each of a thousand tons, which could be hoisted into the tube and arranged in front of the meli-melonite so as to form a compact charge.