  “I define the limit of a body as the aggregate of all the extreme [äusserst] ether-atoms which still belong to it. […] A closer consideration further shows that many bodies are at certain places altogether devoid of limiting atoms; none of their atoms can be described as the extreme ones among those which still belong to it and would accompany it if it started to move. [Two bodies are in contact] when the extreme atoms of the one, […] together with certain atoms of the other, form a continuous extension.” [Bernard Bolzano Paradoxes of the Infinite, § 66 (1851: 167–168)]