I'm pretty sure he's talking about the testability of science; when you have a theory, it's not science until it becomes a testable observation. At one point, p

I'm pretty sure he's talking about the testability of science; when you have a theory, it's not science until it becomes a testable observation. At one point, presumably, the early model of physics allows "naturalists" to make predictions on the color of gold based on the information of chemical elements. And the color was supposed to be platinum. Therefore, the theory was not quite right, and naturalists of the time could conclude that their model was incomplete. I don't think anyone was ever doubting the true color of gold.