in so far as I think of it only in contact, in accordance with common experience by which it is hardly perceived at small distances. Cohesion is commonly assumed as an altogether universal property of matter, not because we are led to it through the mere conception of a matter, but because experience presents it everywhere. But this universality must not be understood collectively, as though every matter, through this kind of attraction, acted at the same time on every other [matter] in the universe—in the same way as gravitation—but merely disjunctively, namely on one or the other, it does not signify what kind of matters they may be, that come in contact with it. For this reason, and since this attraction, as is demonstrable on various grounds, is not a penetrating but only a superficial force, inasmuch as it is not itself regulated on all sides according to the density—since to complete strength of cohesion a preceding state of fluidity of the matters and their subsequent solidification is requisite, and the closest contact of broken but hard matters in the same surfaces, with which they previously firmly cohered (as for instance a looking-glass where there is a crack), do not any longer admit the degree of attraction which they received on solidifying after their fluid [state—for this reason I hold this attraction in contact to be no fundamental force of matter, but only a derivative one; of which more hereafter. A matter whose parts, notwithstanding their strong cohesion among one another, can be impelled by every moving force—be it never so small—past one another, is fluid. But parts of a matter are impelled past one another, if, without diminishing the quantum of contact, they are obliged to change [places] among one another. Parts, in other words, matters, are separated if their contact is not merely changed with others but destroyed, or its quantum diminished. A firm—better a solid—body (corpus rigidum) is that whose parts cannot be impelled past one another by every force, and which consequently resist impulsion with a certain degree of force.
The obstacle to the impulsion of matters past one another is friction.
The resistance to separation of matters in contact is cohesion. Fluid matters, therefore, suffer no friction in their division; but where this is met with, the matters
