Pierre Curie

the constitution of the medium but also its condition of movement and the physical agents to which it is subordinated.

The same thing is true for the conduction of heat or electricity, for magnetization, for polarization, etc.

It was the study of optics which first showed that the propagation of light in a crystal is dependent upon the elements of symmetry in that crystal

Nature furnishes us the idea of a plane of symmetry and of an axis of symmetry.

a condition of space characteristic of the medium in which a given phenomenon occurs.

Thus a regular flower of four petals has an axis of symmetry of the order four, or a quarternary axis

perfect in the case of crystallized minerals

only imperfectly any regular dispositions in the aspects of animals and plants

perfect in the case of crystallized minerals.

only imperfectly any regular dispositions in the aspects of animals and plants.