 Indeed, in the Dialogus Physicus Hobbes, speaking through speaker A, often granted the observational reports of the experimenters without question. For example, speaker A does not question what the experimenters claim they observed regarding a bladder that had been placed inside the air-pump and weighed, noting “They can be certain that the scale in which the bladder is, is more depressed than the other, their eyes bearing witness” (DP 369; OL IV.261). Instead of criticizing the experimenters’ reliance upon observations, speaker A argues that the experimenters cannot know, in the case of this explanation, what the cause of the scale being depressed is because their posited cause (the “natural gravity” of the air) does not allow them to explain why the scale is depressed after the air-pump is engaged. In contrast, speaker A offers a possible cause that is borrowed, with an explicit citation, from Hobbes’ geometrical account of “simple circle motion” and “fermentation” developed in De Corpore 21.5 (Adams 2017).