 Secondly, Boyle takes himself to have shown that, for atmospheric air, within the limits of his experimental set-up, “the pressures and expansions [are] in reciprocal proportion,” or, as we would say, pressure and volume vary inversely. He doesn’t take himself to have shown anything more than this. He does remark that further experiments may show that the relationship holds outside the boundary conditions imposed by the experimental set-up, but the experiments he has just made certainly don’t show that. What Boyle expressly said was,