We need not linger over the Roman candle of No. 12, or the rocket of No. 13: had their charges been explosive there would have been an end of the candle and rocket, and of the men who fired them. The cracker of No. 13 was a toy intended to “go off with a bang,” without hurt to the bystanders. The case was to be as strong as possible and securely fastened at both ends with iron wires. It was to be half filled with rocket composition, a mixture which burned in a cracker-case precisely as it burned in a rocket-case—with progressive combustion. Now Roger Bacon had a similar toy, constructed with the very same object, _i.e._ “to go off with a bang,” the case of which was “merely a bit of paper.” Why was there this marked difference, then, between the two cases? Because the noise was produced in the one by the explosion of the charge and in the other by the rupture of the case. Bacon’s charge (as will be shown in Chap. viii.) was gunpowder, and the required “bang” was directly produced by its explosion. Marcus’ toy was charged with an incendiary, the combustion of which did not produce a “bang” directly, but which produced one indirectly by ultimately bursting open the thick, stout case. The gases generated by its combustion “gradually developed until the case burst,”[179] just as a bladder bursts “with a bang” when over-inflated. Had Bacon’s toy been charged with an incendiary, the case, which was only a sheet of paper, would have been set on fire by the heated gases long before their pressure had reached the bursting point, and there would have been no “bang.” Had Marcus’ toy been charged with an explosive, it would have exploded destructively, and what was intended for a public diversion would have proved a common danger, owing to the thickness of the case and the iron wire coiled round it. There is nothing in the tract to show that its authors had any notion of explosives, and their silence, without any assignable motive, is strong evidence that they knew nothing about them. It is incredible that pyrotechnists who seldom omit to call attention to the effects of their incendiaries,[180] should have failed to make some allusion to explosives if they possessed them. Their silence was not owing to fear of the Church, for the decree of the Second Council of the Lateran was directed against the very mixtures which form the staple of the _Liber Ignium_, incendiaries.[181] The 12th and 13th recipes contain the ingredients of the future gunpowder; they form the last link in the long chain of evolution which connects the incendiaries of primitive times with gunpowder; but they were not gunpowder, because they did not explode. The chrysalis, we know, will become a butterfly if it lives; nevertheless it would be an abuse of language and a misrepresentation of fact to call it a butterfly.