II
§ 3. We may distinguish between essential properties,
without which a body cannot be thought of as existing (exten
sion and impenetrability), and accidental ones.
§ 4. 1) Extension or magnitude 8-11. Mass, Volume,
Form of a body, Measure, its unit the metre.
§ 5. 2) Impenetrability. The space occupied by one
body cannot simultaneously be occupied by another. Seeming
penetrability (water poured upon a heap of sand) 12-17.
§ 6. 3) Porosity. Bodies never fill the whole space they
occupy. The pores are either sensible 18. 19. 20. 21. or inter
molecular pores.
Examples: 18-30. Besides these: Chalk thrown into water;
filters (Chem. Primer, page 38); salt dissolved in water.
§ 7. A consequence of porosity is the Compressibility of
bodies. Hence: The density of a body (its mass being un
changed) increases in proportion to the decrease of its volume.
If D = density of body, M its mass and V its volume, and d, m
and v the corresponding figures for another body, we may say:
D: d=M. v: m.V or D = M/V.
§ 8. 4) Divisibility. 31-35. All bodies may be divided
into distinct parts. Some facts in Chemistry lead to the con
clusion, that the divisibility of matter has a limit, while further
consideration has led to the supposition of the existence of the
so-called Atoms (extremely minute indivisible parts). Certain
phenomena indicate further, that these atoms do not come in
contact with each other, but each of them is supposed to be sur
rounded by an ether-atmosphere (ether means an extremely fine
gaseous substance).
Remark. The existence of Atoms represents a dogma in natural
science; for the atoms are beyond the reach of experiments. To proceed
