"Cast iron is very brittle, though," replied Morgan. "Yes, but it possesses great resistance. I will now ask our worthy secretary to calculate the weight of a cast-iron gun with a bore of nine feet and a thickness of six feet of metal." "In a moment," replied Maston. Then, dashing off some algebraical formulæ with marvellous facility, in a minute or two he declared the following result:— "The cannon will weigh 68,040 tons. And, at two cents a pound, it will cost—?" "2,510,701 dollars." Maston, the major, and the general regarded Barbicane with uneasy looks. "Well, gentlemen," replied the president, "I repeat what I said yesterday. Make yourselves easy; the millions will not be wanting." With this assurance of their president the Committee separated, after having fixed their third meeting for the following evening. CHAPTER IX. THE QUESTION OF THE POWDERS. There remained for consideration merely the question of powders. The public awaited with interest its final decision. The size of the projectile, the length of the cannon being settled, what would be the quantity of powder necessary to produce impulsion? It is generally asserted that gunpowder was invented in the fourteenth century by the monk Schwartz, who paid for his grand discovery with his life. It is, however, pretty well proved that this story ought to be ranked amongst the legends of the middle ages. Gunpowder was not invented by any one; it was the lineal successor of the Greek fire, which, like itself, was composed of sulphur and saltpetre. Few persons are acquainted with the mechanical power of gunpowder. Now this is precisely what is necessary to be understood in order to comprehend the importance of the question submitted to the committee. A litre of gunpowder weighs about 2 lbs.; during combustion it produces 400 litres of gas. This gas, on being liberated and acted upon by a temperature raised to 2400 degrees, occupies a space of 4000 litres: consequently the volume of powder is to the volume of gas produced by its combustion as 1 to 4000. One may judge, therefore, of the tremendous pressure of this gas when compressed within a space 4000 times too confined. All this was, of course, well known to the members of the committee when they met on the following evening. The first speaker on this occasion was Major Elphinstone, who had been the director of the gunpowder factories during the war. Illustration: THE INVENTION OF GUNPOWDER BY THE MONK SCHWARTZ. "Gentlemen," said this distinguished chemist, "I begin with some figures which will serve as the basis of our calculation. The old 24-pounder shot required for its discharge 16 lbs. of powder." "You are certain of the amount?" broke in Barbicane.