The Solid State
Solid bodies are characterized by the existence of a definite shape in virtue of which one is able to recognize them individually. It is the solid state of aggregation which has guarded solid body's secrets most obstinately. The constituent particles of a solid body are fixed relatively to one another, and this of course necessitates a definite form and volume. All solid bodies possess a certain degree of form and volume elasticity so that they can transmit both transverse and longitudinal waves. The forces of cohesion are also more marked in solids than in liquids; these forces are responsible for the definite shape of solid bodies. Solids fill space and produce the same degree of compactness as do liquids, for in general only small changes in density occur when bodies are melted or solidified. In crystals the forces of cohesion imply limits to the shape which the solids can assume.