They know not the art of granulating the paste, as in Europe, but use it in a coarse powder, which sometimes cakes together into a solid mass; and from the impurity of the nitre, (no means appearing to be employed for extracting the common salt it usually contains) the least exposure to the air, by attracting the moisture, makes it unfit for service. This may be one reason for their objection to firelocks. It has been remarked, that the three great discoveries of the magnetic needle, of gunpowder, and of printing, in Europe, followed close upon the return of the famous traveller Marco Polo. It was the boast indeed of _Caung-shee_ to the Jesuits, when they instructed him in some of the sciences of Europe, that the latter country was neither acquainted with the mariner's compass, nor with the art of printing, nor with gunpowder, till they had been in common use in China near two thousand years. As to gunpowder, it is pretty obvious, that our countryman Roger Bacon was well acquainted with the ingredients that enter into its composition. In more than one part of his works he observes, that with saltpetre and other articles may be made a fire that will inflame to a great distance; and in one place he states, that with sulphur, saltpetre, and something else, which he disguises under two or three barbarous words, a composition may be made, by which the effects of thunder and of lightning may be imitated. Bacon died in the year 1292, and Marco Polo returned to Europe in 1295; so that he could not possibly have received any hint to lead towards the discovery through the channel of the Venetian traveller[18]. [18] The invention, in Europe, is usually attributed to one Schwartz, a German Monk, about the year 1354, which, however, is very doubtful, as there is every reason to believe that cannon was made use of at the battle of Cressy, which happened in the year 1346. And Mariana, in his account of the siege of Algeziras by the Spaniards, in the year 1342, or 1343, as quoted by Bishop Watson, observes, "that the Moors very much annoyed the Christians with their iron shot;" and he further adds, that "this is the first mention made in history of the use of gunpowder and ball." It is therefore extremely probable, that the first introduction of gunpowder into Europe was by some Mahomedans from the eastward, and that Schwartz was not the inventor, although he might perhaps have been the first publisher of the discovery.