7. In Chemistry, new substances have of late had names assigned them from Greek roots, as _Iodine_, from its violet colour, _Chlorine_ from its green colour. In like manner fluorine has by the French chemists been called _Phthor_, from its destructive properties. So the {326} new metals, _Chrome_, _Rhodium_, _Iridium_, _Osmium_, had names of Greek derivation descriptive of their properties. Some such terms, however, were borrowed from localities, as _Strontia_, _Yttria_, the names of new earths. Others have a mixed origin, as _Pyrogallic_, _Pyroacetic_, and _Pyroligneous_ Spirit. In some cases the derivation has been extravagantly capricious. Thus in the process for making Pyrogallic Acid, a certain substance is left behind, from which M. Braconnot extracted an acid which he called _Ellagic_ Acid, framing the root of the name by reading the word _Galle_ backwards. The new laws which the study of Electro-chemistry brought into view, required a new terminology to express their conditions: and in this case, as we have observed in speaking of the Twelfth Maxim, arbitrary words are less suitable. Mr. Faraday very properly borrowed from the Greek his terms _Electrolyte_, _Electrode_, _Anode_, _Cathode_, _Anïon_, _Cathïon_, _Dielectric_. In the mechanico-chemical and mechanical sciences, however, new terms are less copiously required than in the sciences of classification, and when they are needed, they are generally determined by analogy from existing terms. _Thermo-electricity_ and _Electro-dynamics_ were terms which very naturally offered themselves; Nobili's _thermo-multiplier_, Snow Harris's _unit-jar_, were almost equally obvious names. In such cases, it is generally possible to construct terms both compendious and descriptive, without introducing any new radical words.