 Like Poincaré, Boltzmann’s answer to historical pessimism was that despite the presence of “revolutions” in science, there is enough continuity in theory change to warrant the claim that some “achievements may possibly remain the possession of science for all time” (1901: 253). But unlike Poincaré, Boltzmann did not restrict the criterion of invariance-in-theory-change to relations only: The answer to the historical challenge is to look for patterns of continuity in theory change. In fact, as Boltzmann noted, if the historical principle is correct at all, it cuts also against the equations of the phenomenologists. For unless these very equations remain invariant through theory-change, there should be no warrant for taking them to be accurate descriptions of worldly relations (cf. 1901: 253). Besides, Boltzmann noted, the very construction of the differential equations of the phenomenologists requires commitment to substantive atomistic assumptions. Hence, the phenomenologists are not merely disingenuous when they jettison the atomistic assumptions after the relevant differential equations have been arrived at. Their move is self-undermining. In light of the historical principle, the success of the mathematical equations would lead to their defeat, since the very theory that led to this success would fall foul of the historical principle: it would have to be abandoned.