Mach's Elementenlehre as a theory of physical elements found much of its inspiration in the burgeoning field of German psychology, in which he was intimately involved as a researcher. In the works of Herbart, Lotze, Wundt, and others, Mach was exposed to a very sophisticated philosophico-psychological tradition devoted to a problem that also faced his theory of elements. Given that the world consisted for him of extensionless elements and spaceless-timeless functional relationships, how could one explain the fact that the world appears to be spread out in space and time before us, both in physics (where brute extension is assumed as given) and in psychology (where an explanation of the extended sensory manifolds is sought)? Could one actually somehow construct extension logically from simpler notions of intensity or quality similar to color or sound?