investigations of others seeks to snatch a most empty glory. Verily_ Envy detracts from great Homer's genius; _but_ Whoever thou art, Zoilus, thou hast thy name from him. _May your new physiology of the Magnet, I say (kept back for so many years), come forth now at length into the view of all, and your Philosophy, never to be enough admired, concerning the great Magnet (that is, the earth); for, believe me_ (If there is any truth in the forebodings of seers), _these books of yours on the Magnet will avail more for perpetuating the memory of your name than the monument of any great Magnate placed upon your tomb._ {vj} * * * * * _Interpretation of certain words.[1]_ Terrella, a globular loadstone. Verticity, polar vigour, not [Greek: peridinêsis] but [Greek: peridineisios dunamis]: not a vertex or [Greek: polos] but a turning tendency. Electricks, things which attract in the same manner as amber. Excited Magnetick, that which has acquired powers from the loadstone. Magnetick Versorium, a piece of iron upon a pin, excited by a loadstone. Non-magnetick Versorium, a versorium of any metal, serving for electrical experiments. Capped loadstone, which is furnished with an iron cap, or snout. Meridionally, that is, along the projection of the meridian. Paralleletically, that is, along the projection of a parallel. Cusp, tip of a versorium excited by the loadstone. Cross, sometimes used of the end that has not been touched and excited by a loadstone, though in many instruments both ends are excited by the appropriate termini of the stone. Cork, that is, bark of the cork-oak. Radius of the Orbe of the Loadstone, is a straight line drawn from the summit of the orbe of the loadstone, by the shortest way, to the surface of the body, which, continued, will pass through the centre of the loadstone. Orbe of Virtue, is all that space through which the Virtue of any loadstone extends. Orbe of Coition, is all that space through which the smallest magnetick is moved by the loadstone. Proof, for a demonstration shown by means of a body. Magnetick Coition: since in magnetick bodies, motion does not occur by an attractive faculty, but by a concourse or concordance of both, not as if there were an [Greek: helktikê dunamis] of one only, but a [Greek: sundromê] of both; there is always a coition of the vigour: and even of the body if its mass should not obstruct. Declinatorium, a piece of Iron capable of turning about an axis, excited by a loadstone, in a declination instrument. * * * * * INDEX OF CHAPTERS. _Book 1._ Chap. 1. Ancient and modern writings on the Loadstone, with certain matters of mention only, various opinions, & vanities. Chap. 2. Magnet Stone, of what kind it is, and its discovery. Chap. 3. The loadstone has parts distinct in their natural power, & poles conspicuous for their property.