 This relational answer to historical pessimism was motivated, at least partly, by the widespread scepticism towards the atomic theory of matter. Atomism posited the existence of unobservable entities—the atoms—to account for a host of observable phenomena (from chemical bonding to Brownian motion). A trend among scientists opposed to the explanation of the visible in terms of the invisible was what Ludwig Boltzmann called “phenomenologists” (which included the early Max Planck), according to whom the aim of science was to “write down for every group of phenomena the equations by means of which their behavior could be quantitatively calculated” (Boltzmann 1901: 249). The theoretical hypotheses from which the equations might have been deduced were taken to be the scaffolding that was discarded after the equations were arrived at. For phenomenologists, then, hypotheses are not unnecessary or useless—rather they have only a heuristic value: they lead to stable (differential) equations and that’s it.