Gilbert's glossary is practically an apology for the introduction into the Latin language of certain new words, such as the nouns _terrella_, _versorium_, and _verticitas_, and the adjectival noun _magneticum_, which either did not exist in classical Latin or had not the technical meaning which he now assigns to them. His _terrella_, or [Greek: mikrogê], as he explains in detail on p. 13, is a little magnetic model of the earth, but in the glossary he simply defines it as _magnes globosus_. Neither _terrella_ nor _versorium_ appears in any Latin dictionary. No older writer had used either word, though Peter Peregrinus (_De Magnete_, Augsburg, 1558) had described experiments with globular loadstones, and pivotted magnetic needles suitable for use in a compass had been known for nearly three centuries. Yet the pivotted needle was not denominated _versorium_. Blondo (_De Ventis_, Venice, 1546) does not use the term. Norman (_The Newe Attractiue_, London, 1581) speaks of the "needle or compasse," and of the "wyre." Barlowe (_The Navigators Supply_, London, 1597) speaks of { 2} the "flie," or the "wier." The term _versorium_ (literally, the _turn-about_) is Gilbert's own invention. It was at once adopted into the science, and appears in the treatises of Cabeus, _Philosophia Magnetica_ (Ferrara, 1629), and of Kircher, _Magnes sive de Arte Magnetica_ (Coloniæ, 1643), and other writers of the seventeenth century. Curiously enough, its adoption to denote the pivotted magnetic needle led to the growth of an erroneous suggestion that the mariners' compass was known to the ancients because of the occurrence in the writings of Plautus of the term _versoriam_, or _vorsoriam_. This appears twice as the accusative case of a feminine noun _versoria_, or _vorsoria_, which was used to denote part of the gear of a ship used in tacking-about. Forcellini defines _versoria_ as "funiculus quo extremus veli angulus religatur"; while _versoriam capere_ is equivalent to "reverti," or (metaphorically) "sententiam mutare." The two passages in Plautus are:
EUT. Si huc item properes, ut istuc properas, facias rectius, Huc secundus ventus nunc est; cape modo vorsoriam; Hic Favonius serenu'st, istic Auster imbricus: Hic facit tranquillitatem, iste omnes fluctus conciet. (in _Mercat._ Act. V., sc. 2.)