For example, he constantly refers to force under such names as virtus, species, imago, agentis, and a score of other names, and this naturally gives rise to the great differences in the interpretations of his writings, with corresponding differences in estimates of them.
The claim that Bacon originated the use of lenses, in the form of spectacles, cannot be proven.

Smith has determined that as early as the opening years of the fourteenth century such lenses were in use, but this proves nothing as regards Bacon's connection with their invention.
The knowledge of lenses seems to be very ancient, if we may judge from the convex lens of rock crystal found by Layard in his excavations at Nimrud.

There is nothing to show, however, that the ancients ever thought of using them to correct defects of vision.

Neither, apparently, is it feasible to determine whether the idea of such an application originated with Bacon.
Another mechanical discovery about which there has been a great deal of discussion is Bacon's supposed invention of gunpowder.

It appears that in a certain passage of his work he describes the process of making a substance that is, in effect, ordinary gunpowder; but it is more than doubtful whether he understood the properties of the substance he describes.