[28] It is in the “Epistle Dedicatorie” to this work that Barlowe is shown to have been the first to make use of the word magnetisme.
[29] “Imperial Dict. of Universal Biography,” Vol. II. p. 626.
[30] The earth itself is a magnet according to Gilbert, who considered that the inflections of the lines of equal declination and inclination depend upon the distribution of mass, the configuration of continents, or the form and extent of the deep, intervening ocean basins. It is difficult to connect the periodic variations which characterize the three principal forms of magnetic phenomena (the isoclinic, the isogonic and the isodynamic lines) with this rigid system of the distribution of force and mass, unless we represent to ourselves the attractive force of the material particles modified by similar periodic changes of temperature in the interior of the terrestrial planet.... Of these lines, the isogonic are the most important in their immediate application to navigation, whilst we find from the most recent views that the isodynamic, especially those which indicate the horizontal force, are the most valuable elements in the theory of terrestrial magnetism (Humboldt, “Cosmos,” 1859–1860, Vol. I. pp. 180–181, 185; Vol. II. p. 334, wherein references are made to Gauss, “Resultate der Beob. des Magn. Vereins,” 1838, s. 21; Sabine, “Report on the Variations of the Magnetic Intensity,” p. 63).
[31] The reader is referred to Appendix I herein for “Accounts of early writers and others alluded to in Gilbert’s ‘De Magnete,’ not already disposed of throughout this Bibliographical History.” Gilbert says that only a few points touching the loadstone are briefly mentioned by Marbodeus Gallus, Albertus, Mattæus Silvaticus, Hermolaus Barbarus, Camillus Leonhardus, Cornelius Agrippa, Fallopius, Joannes Langius, Cardinal de Cusa, Hannibal Rosetius Calaber, all of whom repeat only the figments of others.
[32] Sir Kenelm Digby (“Treatise of the Nature of Bodies,” 1645, Chap. XX. p. 225) says that the manner in which Gilbert “arrived to discover so much of magnetical philosophy” and “all the knowledge he got on the subject, was by forming a little loadstone into the shape of the earth. By which means he composed a wonderful designe, which was to make the whole globe of the earth maniable; for he found the properties of the whole earth in that little body ... which he could manage and try experiments upon at his will....” In the note at p. 47 (P. Peregrinus, A.D. 1269), it will be seen that the terrella was constructed by both in practically the same manner: only Peregrinus considered it “a likeness to the heavens,” whilst Gilbert regarded it as the earth itself.
[33] The magnetized versorium consisted of a piece of iron, or needle, resting upon a point, or pin, and was put in motion, excited, by the loadstone or natural magnet. The non-magnetized versorium was made of any sort of metal, for use in electrical experiments (“De Magnete,” Book II. chap. ii.; Book III. chap. i.).
[34] Asterisks. As Gilbert remarks in his Author’s Preface, he has set over against “the great multitude” of his discoveries and experiments larger and smaller asterisks according to their importance and their subtility; all of his experiments having been, says he, “investigated and again and again done and repeated under our eyes.” There are, in all, 178 small and 21 large asterisks, some of them being attached to illustrations, of which latter there are as many as 84 throughout the work. See Appendix II herein.
[35] Humboldt, “Cosmos,” 1849, Vol. I. p. 170, and Vol. II. pp. 717–718.
[36] Sir Wm. Thomson, “Good Words,” 1879, p. 445.
We have already indicated several modes of construction, notably at A.D. 1282 (Baïlak of Kibdjak), at A.D. 1558 (G. B. Porta), as well as at A.D. 1597 (Wm. Barlowe), and it is interesting to observe how all these vary, more particularly from the types described by Levinus Lemnius in the “De Occulta Naturæ Miracula,” mentioned at B.C. 1033, and by Martinus Lipenius in his “Navigatio Salomonis Ophiritica” noted at A.D. 1250.