more matter: in both cases the difference depends upon the intensity of the acting force; for Kant (following Priestley) has quite correctly reduced matter to forces. But even if the analogy here set up should not be admitted as valid, and it should be insisted upon that the difference of specific gravity can only have its ground in porosity, even this assumption would always lead, not to atoms, but only to a perfectly dense matter, unequally distributed among different bodies; a matter which would certainly be no longer _compressible_, when no pores ran through it, but yet, like the space which it fills, would always remain infinitely _divisible_. For the fact that it would have no pores by no means involves that no possible force could do away with the continuity of its spatial parts. For to say that everywhere this is only possible by extending the already existing intervals is a purely arbitrary assertion. The assumption of atoms rests upon the two phenomena which have been touched upon, the difference of the specific gravity of bodies and that of their compressibility, for both are conveniently explained by the assumption of atoms. But then both must also always be present in like measure, which is by no means the case. For, for example, water has a far lower specific gravity than all metals properly so called. It must thus have fewer atoms and greater interstices between them, and consequently be very compressible: but it is almost entirely incompressible. The defence of atoms might be conducted in this way. One may start from porosity and say something of this sort: All bodies have pores, and therefore so also have all parts of a body: now if this were carried out to infinity, there would ultimately be nothing left of a body but pores. The refutation would be that what remained over would certainly have to be assumed as without pores, and so far as absolutely dense, yet not on that account as consisting of absolutely indivisible particles, atoms; accordingly it would certainly be absolutely incompressible, but not absolutely indivisible. It would therefore be necessary that it should be asserted that the division of a body is only possible by penetrating into its pores; which, however, is entirely unproved. If, however, this is assumed, then we certainly have atoms, _i.e._, absolutely indivisible bodies, thus bodies of such strong cohesion of their spatial parts that no possible power can separate them: but then one may just as well assume such bodies to be large as small, and an atom might be as big as an ox, if it only would resist all possible attacks upon it. Imagine two bodies of very different kinds, entirely freed from all pores by compression, as by means of hammering, or by pulverisation;—would their specific gravity then be the same? This would be the criterion of dynamics. Chapter XXIV. On Matter.