What the paper sets out to show, and what would decide it
On the molecular-kinetic theory of heat, bodies just large enough to see in a microscope must move by amounts a microscope can detect. Einstein thinks this may be the Brownian motion, but says the reports he could obtain were too imprecise for him to judge. Observing the motion and its laws would mean classical thermodynamics is not exactly valid for spaces a microscope can resolve and would allow the size of atoms to be determined; a failed prediction would weigh heavily against the molecular view.