8. The subject of Crystallography has inevitably given rise to many new terms, since it brings under our notice a great number of new relations of a very definite but very complex form. Haüy attempted to find names for all the leading varieties of crystals, and for this purpose introduced a great number of new terms, founded on various analogies and allusions. Thus the forms of calc-spar are termed by him _primitive_, _equiaxe_, _inverse_, _metastatique_, _contrastante_, _imitable_, _birhomboidale_, _prismatique_, _apophane_, _uniternaire_, _bisunitaire_, _dodécaèdre_, _contractée_, _dilatée_, _sexduodecimale_, _bisalterne_, _binoternaire_, and many others. The {327} want of uniformity in the origin and scheme of these denominations would be no valid objection to them, if any general truth could be expressed by means of them: but the fact is, that there is no definite distinction of these forms. They pass into each other by insensible gradations, and the optical and physical properties which they possess are common to all of them. And as a mere enunciation of laws of form, this terminology is insufficient. Thus it does not at all convey the relation between the _bisalterne_ and the _binoternaire_, the former being a combination of the _metastatique_ with the _prismatique_, the latter, of the _metastatique_ with the _contrastante_: again, the _contrastante_, the _mixte_, the _cuboide_, the _contractée_, the _dilatée_, all contain faces generated by a common law, the index being respectively altered so as to be in these cases, 3, 3/2, 4/5, 9/4, 5/9; and this, which is the most important geometrical relation of these forms, is not at all recorded or indicated by the nomenclature. The fact is, that it is probably impossible, the subject of crystallography having become so complex as it now is, to devise a system of names which shall express the relations of form. Numerical symbols, such as those of Weiss or Naumann, or Professor Miller, are the proper ways of expressing these relations, and are the only good crystallographic terminology for cases in detail. The terms used in expressing crystallographic laws have been for the most part taken from the Greek by all writers except some of the Germans. These, we have already stated, have constructed terms in their own language, as _zwei-und-ein gliedrig_, and the like. In Optics we have some new terms connected with crystalline laws, as _uniaxal_ and _biaxal_ crystals, _optical axes_, which offered themselves without any effort on the part of the discoverers. In the whole history of the undulatory theory, very few innovations in language were found necessary, except to fix the sense of a few phrases, as _plane-polarized_ light in opposition to _circularly-polarized_, and the like.