Roger Bacon made one of the earliest mentions of gunpowder in Europe in 1267, in his work Epistola de secretis operibus artiis et naturae.[32] His studies of gunpowder greatly improved the range of rockets.[7] Bacon has been credited by some authors as the inventor of gunpowder (although the first to use it were Chinese), because around 1261 he developed the correct formula for gunpowder (75% of saltpeter, 15% of carbon and 10% of sulphur).[33] Jean Froissart had the idea of launching rockets through tubes, so that they could make more accurate flights. Froissart's idea is a forerunner of the modern bazooka.[7]