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Larger mineral masses exhibit degrees of porosity not less striking. Water percolates through the sides and roofs of caverns and grottoes, and being impregnated with calcareous and other earths, forms stalactites, or pendant protuberances, which present a curious appearance.

(23.) Compressibility.—That quality, in virtue of which a body allows its volume to be diminished without diminishing its mass, is called compressibility. This effect is produced by bringing the constituent particles more close together, and thereby increasing the density and diminishing the pores. This effect may be produced in several ways; but the name “compressibility” is only applied to it when it is caused by the agency of mechanical force, as by pressure or percussion.

All known bodies, whatever be their nature, are capable of having their dimensions reduced without diminishing their mass; and this is one of the most conclusive proofs that all bodies are porous, or that the constituent atoms are not in contact; for the space by which the volume may be diminished must, before the diminution, consist of pores.