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In bodies which are constituted uniformly throughout their entire dimensions, the component particles and the pores are uniformly distributed through the volume; that is, a given space in one part of the volume will contain the same quantity of matter and the same quantity of pores as an equal space in another part.

(20.) The proportion of the quantity of matter to the magnitude is called the density. Thus if of two substances, one contain in a given space twice as much matter as the other, it is said to be “twice as dense.” The density of bodies is, therefore, proportionate to the closeness or proximity of their particles; and it is evident, that the greater the density, the less will be the porosity.

The pores of a body are frequently filled with another body of a more subtle nature. If the pores of a body on the surface of the earth, and exposed to the atmosphere, be greater than the atoms of air, then the air may pervade the pores. This is found to be the case with many sorts of wood which have an open grain. If a piece of such wood, or of chalk, or of sugar, be pressed to the bottom of a vessel of water, the air which fills the pores will be observed to escape in bubbles and to rise to the surface, the water entering the pores, and taking its place.