Gunpowder was known to Roger Bacon and Albertus Magnus about 1250, but... I conclude that both obtained a knowledge of it from Arabic sources. - J. R. Partington

We perceive clearly that theories and hypotheses are not accepted or rejected outright; they have their periods of activity, and then lie dormant for a time, only to be revived in a new form later on.

Some recent short publications on Chinese gunpowder and firearms are misleading... I have had valuable assistance from Dr. J. Needham... If the dates of the texts are correct, the discovery of the use of saltpetre in explosives and the development of gunpowder are to be sought in China from the eleventh century. The history of gunpowder is associated with that of saltpetre, no comprehensive account of which was available.

The statement of a law of nature involves the formation of a concept, or general idea, in which the likenesses of phenomena are collected, and the differences, in so far as they are not intimately involved in the nature of the case, are eliminated.