The igneous bodies of which Bacon speaks fall into two classes. The first class are incendiaries. “Incendiaries,” he tells us, “may be made from saltpetre, or petroleum, or maltha,[372] or naphtha, mixed with other substances.... To these are allied Greek fire and many other incendiaries[373].... (Burning) maltha, if thrown upon an armed soldier, will cause his death.... It is difficult to extinguish, water being useless for this purpose.”[374] But side by side with these passages we find descriptions of igneous compositions of a totally different kind. “There are other natural wonders. We can produce in the air sounds loud as thunder and flashes bright as lightning—nay, even surpassing the powers of nature. A small quantity of (a certain) composition, no bigger than one’s thumb, will give forth (on ignition) a deafening noise and a vivid flash.”[375] We have, too, the passage, already quoted, in the eleventh chapter, where he says that saltpetre and sulphur and _something else_ give forth (on ignition) “a thundering noise and a vivid flash.”[376] Again: “Some compositions (when ignited) make an unbearable noise.... No other sound can be compared with it. Others produce flashes more fearful to behold than real lightning.... We may exemplify these effects with a child’s toy which contains within it a quantity of saltpetre (mixture) the size of one’s thumb. In the bursting of this bauble, made only of parchment, there are given forth a noise louder than the mutterings of thunder and a flash brighter than the brightest lightning.”[377] It will be evident on a moment’s consideration that the charge of this toy must have been an explosive. Had it been an incendiary, the paper would have taken fire long before the pressure of the gases generated by the combustion had increased sufficiently to burst the case, and there would have been no loud report. The consequences of igniting these two classes of composition are described so clearly as to preclude all possible misunderstanding:—the incendiary _burns_ fiercely, while the other mixture gives forth _a bright flash and a loud noise_. In the latter case, Bacon was describing an explosion, and, as he has elsewhere spoken of saltpetre, charcoal, and sulphur, the reasonable conclusion is that the explosive was gunpowder.