1. The generalization of the class ofElectrics.2. The observation that damp weather hinders electrification.3. The generalization that electrified bodies attract everything,including even metals, water, and oil.4. The invention of the non-magneticversoriumor electroscope.5. The observation that merely warming amber does not electrify it.6. The recognition of a definite class ofnon-electrics.7. The observation that certain electrics do not attract if roasted orburnt.8. That certain electrics when softened by heat lose their power.9. That the electric effluvia are stopped by the interposition of a sheetof paper or a piece of linen, or by moist air blown from the mouth.10. That glowing bodies, such as a live coal, brought near excited amberdischarge its power.11. That the heat of the sun, even when concentrated by a burning mirror,confers no vigour on the amber, but dissipates the effluvia.12. That sulphur and shell-lac when aflame are not electric.13. That polish is not essential for an electric.14. That the electric attracts bodies themselves, not the intervening air.15. That flame is not attracted.16. That flame destroys the electrical effluvia.17. That during south winds and in damp weather, glass and crystal, whichcollect moisture on their surface, are electrically more interferedwith than amber, jet and sulphur, which do not so easily take upmoisture on their surfaces.18. That pure oil does not hinder production of electrification or exerciseof attraction.19. That smoke is electrically attracted, unless too rare.20. That the attraction by an electric is in a straight line toward it.[128]Page 48, line 35.Page 48, line 39.quæ sunt illæ materiæ.—Gilbert's list of electrics should be compared with those given subsequently by Cabeus (1629), by Sir Thomas Browne (1646), and by Bacon. The last-named list occurs in hisPhysiological Remains, published posthumously in 1679; it contains nothing new. Sir Thomas Browne's list is given in the following passage, which is interesting as using for the first time in the English language the nounElectricities:"Many stones also both precious and vulgar, although terse and smooth, have not this power attractive; as Emeralds, Pearle, Jaspis, Corneleans, Agathe, Heliotropes, Marble, Alablaster, Touchstone, Flint and Bezoar. Glasse attracts but weakely though cleere, some slick stones and thick glasses indifferently: Arsenic but weakely, so likewise glasse of Antimony, but Crocus Metallorum not at all. Saltes generally but weakely, as Sal Gemma, Alum, and also Talke, nor very discoverably by any frication: but if gently warmed at the fire, and wiped with a dry cloth, they will better discover their Electricities."(Pseudodoxia Epidemica, p. 79.)In thePhilosophical Transactions, vol. xx., p. 384, isA Catalogue of Electrical Bodiesby the late Dr. Rob. Plot. It begins "Non solum succinum," and ends "alumen rupeum," being identical with Gilbert's list except that he calls "Vincentina & Bristolla" by the name "Pseudoadamas Bristoliensis."[129]Page 49, line 25.Page 49, line 30.non dissimili modo.—Themodusoperandiof the electrical attractions was a subject of much discussion; see Cardan,op. citat.[130]Page 51, line 2.Page 51, line 1.appellunt.—This appears to be a misprint forappelluntur.[131]Page 51, line 22.Page 51, line 23.smyris.—Emery. This substance is mentioned on p.22as a magnetic body.[132]Page 52, line 1.Page 51, line 46.gemmæ ... vt Crystallus, quæ ex limpidâ concreuit.See thenoteto p.48.[133]Page 52, line 30.Page 52, line 32.ammoniacum.—Ammoniacum, or Gutta Ammoniaca, is described by Dioscorides as being the juice of a ferula grown in Africa, resembling galbanum, and used for incense."Ammoniackis a kind of Gum like Frankincense; it grows in Lybia, whereAmmon'sTemple was." Sir Hugh Plat'sJewel House of Art and Nature(Ed. 1653, p. 223).[134]Page 52, line 38.Page 52, line 41.duæ propositæ sunt causæ ... materia & forma.—Gilbert had imbibed the schoolmen's ideas as to the relations of matter and form. He had discovered and noted that in the magnetic attractions there was always a verticity, and that in the electrical attractions the rubbed electrical body had no verticity. To account for these differences he drew the inference that since (as he had satisfied himself) the magnetic actions were due toform, that is to say to something immaterial—to an "imponderable" as in the subsequent age it was called—the electrical actions must necessarily be due tomatter. He therefore put forward his idea that a substance to be an electric must necessarily consist of a concreted humour which is partially resolved into an effluvium by attrition. His discoveries that electric actions would not pass through flame, whilst magnetic actions would, and that electric actions could be screened off by interposing the thinnest layer of fabric such as sarcenet, whilst magnetic actions would penetrate thick slabs of every material except iron only, doubtless confirmed him in attributing the electric forces to the presence of these effluvia. See also p.65. There arose a fashion, which lasted over a century, for ascribing to "humours," or "fluids," or "effluvia," physical effects which could not otherwise be accounted for. Boyle's tracts of the years 1673 and 1674 on "effluviums," their "determinate nature," their "strange subtilty," and their "great efficacy," are examples.[135]Page 53, line 9.Page 53, line 11.Magnes vero....—This passage from line9to line24states very clearly the differences to be observed between the magnetical and the electrical attractions.[136]Page 53, line 36.Page 53, line 41.succino calefacto.—Ed. 1633 readssuccinumin error.[137]Page 54, line 9.Page 54, line 11.Plutarchus ... in quæstionibus Platonicis.—The following Latin version of the paragraph inQuæstio sextais taken from the bilingual edition publisht at Venice in 1552, p. 17verso, liber vii., cap. 7 (or,Quæstio Septimain Ed. Didot, p. 1230)."Electrum uero quæ apposita sunt, nequaquàm trahit, quem admodum nec lapis ille, qui sideritis nuncupatur, nec quicquā à seipso ad ea quæ in propinquo sunt, extrinsecus assilit. Verum lapis magnes effluxiones quasdam tum graves, tum etiam spiritales emittit, quibus aer continuatus & iunctus repellitur. Is deinceps alium sibi proximum impellit, qui in orbem circum actus, atque ad inanem locum rediens, ui ferrum fecum rapit & trahit. At Electrum uim quandam flammæ similem & spiritalem continet, quam quidemtritu summæ partis, quo aperiuntur meatus, foras eijcit. Nam leuissima corpuscula & aridissima quæ propè sunt, sua tenuitate atque imbecillitate ad seipsum ducit & rapit, cum non sit adeo ualens, nec tantum habeat ponderis & momenti ad expellendam aeris copiam, ut maiora corpora more Magnetis superare possit & uincere."[138]Page 54, line 16.Page 54, line 18.Gemma Vincentij rupis.—See thenoteto p.48supra, where the nameVincentinaoccurs.[139]Page 54, line 30.Page 54, line 35.orobi.—The editions of 1628 and 1633 readoribi.[140]Page 55, line 34.Page 55, line 42.in euacuati.—The editions of 1628 and 1633 readinevacuati.[141]Page 58, line 21.Page 58, line 25.assurgentem vndam ... declinat ab F.—These words are wanting in the Stettin editions.[142]Page 59, line 9.Page 59, line 9.fluore.—This word is conjectured to be a misprint forfluxubut it stands in all editions.[143]Page 59, line 22.Page 59, line 25.Ruunt ad electria.—This appears to be a slip forelectrica, which is the reading of the editions of 1628 and 1633.[144]Page 60, line 7.Page 60, line 9.tanqmateriales radij.—The suggestion here of materialraysas themodus operandiof electric forces seems to foreshadow the notion of electric lines of force.[145]Page 60, line 10.Page 60, line 12.Differentia inter magnetica & electrica.—Though Gilbert was the first systematically to explore the differences that exist between the magnetic attraction of iron and the electric attraction of all light substances, the point had not passed unheeded, for we find St. Augustine, in theDe Civitate Dei, liber xxi., cap. 6, raising the question why the loadstone which attracts iron should refuse to move straws. The many analogies between electric and magnetic phenomena had led many experimenters to speculate on the possibility of some connexion between electricity and magnetism. See, for example, Tiberius Cavallo,A Treatise on Magnetism, London, 1787, p. 126. Also the three volumes of J. H. van Swinden,Receuil de Mémoires sur l'Analogie de Electricité et du Magnétisme, La Haye, 1784. Aepinus wrote a treatise on the subject, entitledDe Similitudine vis electricæ et magneticæ(Petropolis, 1758). This was, of course, long prior to the discovery, by Oersted, in 1820, of the real connexion between magnetism and the electric current.[146]Page 60, line 25.Page 60, line 31.Coitionem dicimus, non attractionem.—See the remarks, at the outset of these Notes, on Gilbert's definitions of words.[147]Page 60, line 33.Page 61, line 1.Orpheus in suis carminibus.—This passage is in the chapterΛιθικάof Orpheus, verses 301 to 327. SeeNoteto p.11, line19.[148]Page 61, line 15.Page 61, line 19.Platonis in Timæo opinio.—The passage runs (edition Didot, vol. ii., p. 240, or Stephanus, p. 80, C.):Καὶ δὴ καὶ τὰ τῶν ὑδάτων πάντα ῥεύματα ἔτι δὲ τὰ τῶν κεραυνῶν πτώματα καὶ τὰ θαυμαζόμενα ἠλέκτρων περὶ τῆς ἕλξεως καὶ τῶν Ἡρακλείων λίθων, πάντων τούτων ὁλκὴ μὲν οὐκ ἔστιν οὐδένι ποτε, τὸ δὲ κενὸν εἶναι μηδεν περιωθεῖν τε αὑτὰ ταῦτα εἰς ἄλληλα, τό τε διακρινόμενα καὶ συγκρινόμενα πρὸς τήν αὑτῶν διαμειβόμενα ἕδραν ἕκαστα ἰέναι πάντα, τούτοις τοῖς παθήμασι πρὸς ἄλληλα συμπλεχθεῖσι τεθαυματουργημένα τῷ κατὰ τρόπον ζητοῦντι φανήσεται.[149]Page 61, Line 30.Page 61, line 38. The English version of the lines of Lucretius is from Busby's translation.[150]Page 62, line 5.Page 62, line 7.Iohannes Costæus Laudensis.—Joannes Costa, of Lodi, edited Galen and Avicenna. He also wrote aDe universali stirpium Natura(Aug. Taurin., 1578).[151]Page 63, line 3.Page 63, line 4.Cornelius Gemma 10. Cosmocrit.—This refers to the workDe Naturæ Divinis Characterismis ... Libri ii. Avctore D. Corn. Gemma(Antv., 1575, lib. i., cap. vii., p. 123)."Certè vt à magnete insensiles radij ferrum ad se attrahunt, ab echineide paruo pisciculo sistuntur plena nauigia, à catoblepa spiritu non homines solùm, sed & alta serpentum genera interimuntur, & saxa dehiscunt."See also Kircher'sMagneticum Naturæ Regnum(Amsterodami, 1667, p. 172), Sectio iv., cap. iii., De Magnete Navium, quæ Remora seu Echeneis dicitur. See the note to p.7, line21.[152]Page 63, line 6.Page 63, line 7.Guilielmus Puteanus.—Puteanus (Du Puys) wrote a workDe Medicamentorum quomodocunque Purgantium Facultatibus, Libri ii. (Lugd., 1552), in which he talks vaguely about the substantial "form" of the magnet, and quotes Aristotle and Galen.[153]Page 63, line 21.Page 63, line 25.Baptistæ Portæ.—The passage in the translation is quoted from the English version of 1658, pp. 191, 192.[154]Page 64, line 4.Page 64, line 9.Eruditè magis Scaliger.—Gilbert pokes fun at Scaliger, whose "erudite" guess (that the motion of iron to the magnet was that of the offspring toward the parent) is to be found in his bookDe Subtilitate, ad Cardanum, Exercitatio CII. (Lutetiæ, 1557, p. 156bis).[155]Page 64, line 7.Page 64, line 11.Diuus Thomas.—On p.3Gilbert had already spoken of St. Thomas Aquinas as a man of intellect who would have added more about the magnet had he been more conversant with experiments. The passage here quoted is from the middle of Liber vii. of his commentaries on thede Physicaof Aristotle,Expositio Diui Thome Aquinatis Doctoris Angelici super octo libros Physicorum Aristotelis, etc. (Venice, Giunta edition, 1539, p. 96verso, col. 2).[156]Page 64, line 16.Page 64, line 24.Cardinalis etiam Cusanus.—Cardinal de Cusa (Nicolas Khrypffs) wrote a set of dialogues on Statics,Nicolai Cusani de staticis experimentis dialogus(1550), of which an English version appeared in London in 1650 with the title,The Idiot in four books; the first and second of wisdom, the third of the minde, the fourth of statick experiments. By the famous and learned C. Cusanus.In the fourth bookof statick Experiments, Or experiments of the Ballance, occurs (p. 186) the following:"Orat.Tell me, if thou hast any device whereby the vertues of stones may be weighed."Id.I thinke the vertue of the Load-stone might be weighed, if putting some Iron in one scale, and a Load-stone in the other, untill the ballance were even, then taking away the Load-stone, and some other thing of the same weight being put into the scale, the Load-stone were holden over the Iron, so that that scale wou'd begin to rise; by reason of the Load-stones attraction of the Iron, then take out some of the weight of the other scale, untill the scale wherein the iron is, doe sinke againe to the æquilibrium, or equality still holding the Load-stone unmovable as it was; I beleeve that by weight of what was taken out of the contrary scale, one might come proportionably to the weight of the vertue or power of the Load-stone. And in like manner, the vertue of a Diamond, might be found hereby, becausethey say it hinders the Load-stone from drawing of Iron; and so other vertues of other stones, consideration, being alwayes had of the greatnesse of the bodyes, because in a greater body, there is a greater power and vertue."In the 1588 edition of Baptista Porta'sMagiæ Naturalis Libri xx., in lib. vii., cap. xviii., occurs the description of the use of the balance to which Gilbert refers.[157]Page 67, line 21.Page 67, line 22.aëris rigore.—All editions read thus, but the sense seems to requirefrigore.[158]Page 67, line 27.Page 67, line 31.Fracastorius.—See hisDe Sympathia, lib. i., cap. 5 (Giunta edition, 1574, p. 60).[159]Page 68, line 5.Page 68, line 6.Thaletis Milesij.—See thenoteto p.11, line26.[160]Page 68, line 30.Page 68, line 35.Ità coitio magnetica actus est magnetis, & ferri, non actio vnius.—See the introductory remarks to these notes. There is a passage in Scaliger'sDe Subtilitate ad Cardanum(Exercitat. CII., cap. 5, p. 156op. citat.) which may be compared with Gilbert's for its use of Greek terms: "Nã cùm uita dicatur actus animæ, acceptus est abs te actus pro actione. Sed actus ille estἐντελέχεια, nõ autemἔργον. At Magnetis attractio estἔργον, non autẽἐντελέχεια." To which Gilbert retorts: "non actio unius, utriusqueἐντελέχεια; nonἔργον,συνεντελέχειαet conactus potius quam sympathia." He returns on p.70to the attack on Scaliger's metaphysical notions. There is a parallel passage in theEpitome Naturalis Scientiæof Daniel Sennert (Oxoniæ, 1664), in the chapterDe Motu.[161]Page 71, line 4.Page 71, line 8.vt in 8. physicorum Themistius existimat.—SeeOmnia Themistii Opera(Aldine edition, 1533, p. 63), Book 8 of his Paraphrase on Aristotle'sPhysica.[162]Page 71, line 9.Page 71, line 14.Quod verò Fracastorius.—Op. citat., lib. i., cap. 7, p. 62verso.[163]Page 73, line 2.Page 73, line 2.si A borealis.—The editions of 1628 and 1633 omit the twelve words next following.[164]Page 73, line 9.Page 73, line 11.ex minera.—Minerais not a recognized word, even in late Latin. It occurs again, p.97, line12.[165]Page 77, line 2.Page 77, line 2.multo magis.—This is anà fortioriargument. It is interesting to find Gilbert comparing the velocity of propagation of magnetic forces in space with the velocity of light. The parallel is completed in line 13 by the consideration that as the rays of light require to fall upon an object in order that they may become visible, so the magnetic forces require a magnetic object in order to render their presence sensible.[166]Page 78, line 14.Page 78, line 16.Orbem terrarum distinguunt.—The editions of 1628 and 1633 here add a figure of a globe marked with meridians and parallels of latitude, but with an erroneous versorium pointing to the south. These editions also both readexistentiamfor the wordexistentiumin line20.[167]Page 83, line 5.Page 83, line 5.magnes longior maiora pondera ferri attollit.—Gilbert discovered the advantage, for an equal mass of loadstone, of an elongated shape. It is now well known that the specific amount of magnetism retained by elongated forms exceeds that in a short piece of the same material subjected to equal magnetizing forces.[168]Page 83, line 24.Page 83, line 28.Non obstant crassa tabulata.—Gilbert has several times referred (e.g., on p.77) to the way in which magnetic forces penetrate solid bodies. The experimental investigation in this chapteris the more interesting because it shows that Gilbert clearly perceived the shielding action of iron to be due to iron conducting aside or diverting the magnetic forces.[169]Page 85, line 26.Page 85, line 31.non conveniant.—The editions of 1628 and 1633 both readet conveniant.[170]Page 86, line 3.Page 86, line 3.illud quod exhalat.—Literally,that which exhales, in the sense of that which escapes: but in modern English the verb exhale in the active voice is now not used of the substance that escapes, but is used of the thing which emits it. It must therefore be renderedthat which is exhaled(i.e., breathed out).[171]Page 86, line 13.Page 86, line 15.Ita tota interposita moles terrestris.—Gilbert's notion that the gravitational force of the moon in producing the tides actsthroughthe substance of the earth may seem curiously expressed. But the underlying contention is essentially true to-day. The force of gravity is not cut off or screened off by the interposition of other masses. A recent investigation by Professor Poynting, F.R.S., has shown that so far as all evidence goes all bodies, even the densest, are transparent with respect to gravitational forces.[172]Page 86, line 18.Page 86, line 20.Sed de æstus ratione aliàs.—There is no further discussion of the tides inDe Magnete. But a short account is to be found in Gilbert's posthumous workDe Mundo nostro Sublunari Philosophia nova(Amsterdam, Elzevir, 1651), in Lib. v., the part which in the manuscript was left in English, and was turned into Latin by his brother. It comprises about fifteen quarto pages, from Cap. X. to Cap. XIX. inclusive, beginning with a characteristic diatribe against Taisnier, Levinus Lemnius, and Scaliger. But in assigning causes he himself goes wide of the mark. Proceeding by a process of elimination he first shows that the moon's light cannot be the cause that impels the tides. "Luna," he says, "non radio, non lumine, maria impellit. quomodo igitur? Sane corporum conspiratione, acque (ut similitudine rem exponam) Magnetica attractione." This cryptic utterance he proceeds to explain by a diagram, and adds: "Quare Luna non tam attrahit mare, quàm humorem & spiritum subterraneum; nec plus resistit interposita terra, quàm mensa, aut quicquam aliud densum, aut crassum, magnetis viribus."[173]Page 87, line 7.Page 87, line 9.armatura.—Here this means the cap or snout of iron with which the loadstone was armed. This is apparently the first use of the term in this sense.In theDialogues of Galileo(p. 369 of Salusbury'sMathematical Collections, Dialogue iii.), Sagredus and Salviatus discuss the arming of the loadstone, and the increased lifting power conferred by adding an iron cap. Salviatus mentions a loadstone in the Florentine Academy which, unarmed, weighed six ounces, lifting only two ounces, but which when armed took up 160 ounces. Whereupon Galileo makes Salviatus say: "I extreamly praise, admire, and envy this Authour, for that a conceit so stupendious should come into his minde. ... I think him [i.e., Gilbert] moreover worthy of extraordinary applause for the many new and true Observations that he made, to the disgrace of so many fabulous Authours, that write not only what they do not know, but whatever they hear spoken by the foolish vulgar, never seeking to assure themselves of the same by experience, perhaps, because they are unwilling to diminish the bulk of their Books."[174]Page 87, line 12.Page 87, line 15. The reference tolib.3 isa misprint forlib.2. It is corrected in the edition of 1633, but not in that of 1628.[175]Page 87, line 17.Page 87, line 21.conactu.—The editions of 1628 and 1633 readconatu.[176]Page 88, line 2.Page 88, line 3.Coitio verò non fortior.—This heading to chap. xix., taken with the seven lines that follow, and the contrast drawn betweenunitioandcoitio, throw much light on the fundamental sense attached by Gilbert to the termcoitio. It is here clearly used in the sense ofmutual tendency toward union. Note also the contrasted use in chap. xx. of the verbscohæreandadhære. Adhærence connotes a one-sided force (an impossibility in physics), cohærence a mutual force.[177]Page 90, line 9.Page 90, line 9.nempè vt alter polus maius pondus arripiat.—This acute observation is even now not as well known as it ought to be. Only so recently as 1861 Siemens patented the device of fastening a mass of iron to one end of an electromagnet in order to increase the power of the other end. The fact, so far as it relates to permanent magnets was known to Servington Savery. SeePhilos. Transactions, 1729, p. 295.[178]Page 92, line 3.Page 92, line 4.Suspendit in aëre ferrum Baptista Porta.—Porta's experiment is thus described (Natural Magick, London, 1658, p. 204): "Petrus Pellegrinussaith, he shewed in another work how that might be done: but that work is not to be found. Why I think it extream hard, I shall say afterwards. But I say it may be done, because I have now done it, to hold it fast by an invisible band, to hang in the air; onely so, that it be bound with a small thread beneath, that it may not rise higher: and then striving to catch hold of the stone above, it will hang in the air, and tremble and wag itself."[179]Page 97, line 29.Page 97, line 33.Sed quæri potest ...—The question here raised by Gilbert is whether the lifting-power of magnets of equal quality is proportional to their weight. If a stone weighing a drachm will lift a drachm, would a stone that weighs an ounce lift an ounce? Gilbert erroneously answers that this is so, and that the lifting-power of a loadstone, whether armed or unarmed, is proportional to its mass.The true law of the tractive force or lifting-power of magnets was first given in 1729 by James Hamilton (afterwards Earl of Abercorn) in a work entitledCalculations and Tables Relating to the Attractive Virtue of Loadstones ... Printed[at London?]in the Year1729. (See also a paper in thePhilos. Transactions, 1729-30, vol. xxxvi., p. 245). This work begins thus:"The Principle upon which these Tables are formed, is this: That if TwoLoadstonesare perfectly Homogeneous, that is, if their Matter be of the same Specifick Gravity, and of the same Virtue in all Parts of one Stone, as in the other; and that Like Parts of their Surfaces are Cap'd or Arm'd with Iron; then the Weights they sustain will be as the Squares of the Cube Roots of the Weights of theLoadstones; that is, as their Surfaces."Upon lifting-power see also D. Bernoulli,Acta Helvetica, iii., p. 223, 1758; P. W. Haecker,Zur Theorie des Magnetismus, Nürnberg, 1856; Van der Willigen,Arch. du Musée Teyler, vol. iv., Haarlem, 1878 ; S. P. Thompson,Philos. Magazine, July, 1888.In the book of James Hamilton, p. 5, he mentions a small terrella weighing 139 English grains, which would sustain no less than 23,760 grains, and was valued at £21 13s.10¾d.In theMusæum Septalianumof Terzagus (Dertonæ, 1664, p. 42) is mentioned a loadstone weighing twelve ounces which would lift sixty pounds of iron.Sir Isaac Newton had a loadstone weighing 3 grains, which he wore in a ring. It would lift 746 grains.Thomson'sBritish Annual, 1837, p. 354, gives the following reference: "In theRecords of General Science, vol. iii., p. 272, there is an interesting description of a very powerful magnet which was sent from Virginia in 1776 by the celebrated Dr. Franklin to Professor Anderson, of Glasgow. It is now in the possession of Mr. Crichton. It weighs 2½ grains, and is capable of supporting a load of 783 grains, which is equivalent to 313 times its own weight."[180]Page 99, line 10.Page 99, line 11.Manifestum est.—In this, as in many other passages, Gilbert uses this expression in the sense thatit is demonstrablerather than meaning thatit is obvious: for the fact here described is one that is not at all self-evident, but one which would become plain when the experiment had been tried. For other instances of this use ofmanifestumsee pages144, line20;158, line19;162, line10.[181]Page 100, line 20.Page 100, line 24.si per impedimēta ... pervenire possunt.—All editions agree in this reading, but the sense undoubtedly requiresnon possint. Compare p.91, line21.[182]Page 102, line 4.Page 102, line 4.capite4.—This is a misprint forcapite40, and is retained in the later editions. In the quotation from Baptista Porta, where the English version of 1658 is adhæred to, the words "& deturbat eam" have been omitted by the translator.[183]Page 107, line 16.Page 107, line 18.Cardanus scribit.—The alleged perpetual motion machine is mentioned inDe rerum varietate,lib.9, cap. xlviii. (Basil., 1581, p. 641). See also theNoteto p.223. For Peregrinus and for Taisnier, see thenoteto p.5, lines8and12.[184]Page 107, line 19.Page 107, line 21.Antonij de Fantis.—His work is:Tabula generalis scotice subtilitatis octo Sectionibus vniuersam Doctoris Subtilis Peritiā cōplectēs: ab excellentissimo doctore Antonio de Fātis taruisino edita ...Lugd., 1530.[185]Page 108, line 26.Page 108, line 31.Cusani in staticis.—See thenoteto p.64, line16.[186]Page 108, line 33.Page 108, line 41.Languidi ... tardiùs acquiescunt.—The editions of 1628 and 1633 omit these seven words.[187]Page 109, line 11.Page 109, line 13.halinitro.—Either native carbonate of soda or native carbonate of potash might be meant, but not saltpetre. Scaliger, in hisDe Subtilitate ad Cardanum(Lutet., 1557, p. 164),ExercitatioCIII., 15, under the title,Nitrum non est Salpetræ, says: "More tuo te, tuaque confundis. Salpetræ inter salis fossilis ponis hîc. Mox Halinitrum inter salis, & nitri naturam, speciem obtinere.""Sal nitrumis salt which is boiled out of the earth, especially fat earth, as in stables, or any place of excrements." (A Chymicall Dictionary explaining Hard Places and Words met withall in the Writings of Paracelsus ..., Lond., 1650.)[188]Page 109, line 20.Page 109, line 23.arte ioculatoriâ.—Edition 1628,joculatoriâ; edition 1633,jaculatoriâ.[189]Page 110, line 11.Page 110, line 12.qualis fuit Antonij denarius.—The Elizabethan version of Pliny (book xxxiii., ch. ix., p. 479) runs thus:"To come now unto those that counterfeit money.Antoniuswhiles hee was one of the three usurping Triumvirs, mixed yron with the Romane silver denier. He tempered it also with the brasen coine, and so sent abroad false and counterfeit money."Georgius Agricola (De Natura Fossilium, p. 646) says:"Sed ea fraus capitalis est, non aliter ac eorum qui adulterinas monetas cudunt, argento miscentes multam plumbi candidi portionem, aut etiam ferri, qualis fuit Antonii denarius, ut Plinius memoriæ tradidit. Nunc dicam de candido plumbo, nam majoris pretii est quàm aes. In quod plumbum album, inquit Plinius, addita aeris tertia portione candidi adulteratur stannum."[190]Page 111, line 3.Page 111, line 3.Meminerunt Chatochitis lapis Plinius, atque Iulius Solinus.—The passage in Pliny (English version of 1601, book xxxvii., ch. x., p. 625) runs:"Catochitis is a stone proper unto the Island Corsica: in bignesse it exceedeth ordinarie pretious stones: a wonderfull stone, if all be true that is reported thereof, and namely, That if a man lay his hand thereon, it will hold it fast in manner of a glewie gum."[191]Page 111, line 7.Page 111, line 7.Sagda vel Sagdo.—Albertus Magnus inDe Mineralibus(Venet., 1542, p. 202) says:"Sarda quem alij dicunt Sardo lapis est qui se habet ad tabulas ligni sicut magnes ad ferrū, et ideo adhæret ita fortiter tabulis nauium quòd euelli nō possit, nisi abscindatur cum ipso ea pars tabulæ cui inhæserit, est autē in colore purissimus nitens."And Pliny (op. citat., p. 629):"Sagda is a stone, which the Chaldeans find sticking to ships, and they say it is greene as Porrets or Leekes."[192]Page 111, line 8.Page 111, line 8.Euace.—Evax, king of the Arabs, is said to have written to Nero a treatise on the names, colours, and properties of stones. See thenoteon Marbodæus, p.7, line20.[193]Page 113, line 14.Page 113, line 19.repulsus sit.The words read thus in all editions, but the sense requiresrepulsa sint.[194]Page 113, line 23.Page 113, line 29.Electrica omnia alliciunt cuncta, nihil omninò fugant vnquam, aut propellunt.This denial of electrical repulsion probably arose from the smallness of the pieces of electric material with which Gilbert worked. He could hardly have failed to notice it had he used large pieces of amber or of sealing-wax. Electrical repulsion was first observed by Nicolas Cabeus,Philosophia Magnetica, Ferrara, 1629; but first systematically announced by Otto von Guericke in his treatiseExperimenta Nova (ut vocantur) Magdeburgica, de Vacuo Spatio(Amstel., 1672).[195]Page 113, line 29.Page 113, line 37.cùm de calore quid sit disputabimus.—The discussion of the nature of heat is to be found in Gilbert'sDe Mundo nostro Sublunari(Amstel., 1651), lib. i., cap. xxvi., pp. 77-88.[196]Page 115, line 23.Page 115, line 23.trium vel quatuor digitorum.—Here as in all other places in Gilbert,digitusmeans a finger's breadth, so that three or four digits means a length of two or three inches, or from six to eight centimetres.[197]Page 117, line 26.Page 117, line 25.ille Thebit Bencoræ trepidationis motus."Trepidation in the ancient Astronomy denotes a motion which in the Ptolemaic system was attributed to the firmament, in order to account forseveral changes and motions observed in the axis of the world, and for which they could not account on any other principle." (Barlow'sMathematical Dictionary.)[198]Page 118, line 10.Page 118, line 8.cuspis is aut lilium.—Gilbert usescuspisorliliumalways of the North-pointing end of the needle. Sir Thomas Browne speaks of "the lilly or northern point"; but he differs from Gilbert in saying "thecuspisor Southern point" (Pseudodoxia Epidemica, 1650, p. 46). Only in one place (p.101, line5) does Gilbert speak ofcuspis meridionalis. Everywhere else the south-pointing end is called thecrux.[199]Page 118, line 15.Page 118, line 13.nam æquè potens est.—Later observation showed this view to be incorrect. The horizontal component of the earth's magnetic field is not equally strong all over the globe, and the sluggishness of the needle's return to its position of rest is not due to the supporting pin becoming blunt with wear. The value of the horizontal component is zero at the north magnetic pole, and increases toward the magnetic equator. It is greatest near Singapore and in Borneo, being there more than twice as great as it is at London. (See Captain Creak inReport of Voyage of H.M.S. Challenger, Physics and Chemistry, vol. ii., part vi., 1889.)[200]Page 119, line 5.Page 119, line 2.lapis.—Both Stettin editions readlapidis.[201]Page 119, lines 9-11.Page 119, lines 7-9. The gist of the whole book is summarized in these lines. They furnish a cardinal example of that inductive reasoning which was practist by Gilbert, and of which Bacon subsequently posed as the apostle. Compare pages41and211.[202]Page 120, line 8.Page 120, line 5.dicturi sumus.—Change of verticity is treated of in book iii., chap. x., pp.137to140.[203]Page 125, line 24.Page 125, line 29.appositam.—All editions give this word, though the sense requiresappositum.[204]Page 128, line 9.Page 128, line 11.non nimis longum.—The editions of 1628 and 1633 read (wrongly)minusinstead ofnimis.[205]Page 130, line 12.Page 130, line 14. The wordhuncin the folio of 1600 is corrected in ink totunc, and the Stettin editions both readtunc.[206]Page 132, line 9.Page 132, line 10.minimus & nullius ponderis.—The editions of 1628 and 1633 both wrongly readestfor&.[207]Page 132, line 28.Page 133, line 1.nutat.—The editions of 1628 and 1633 both wrongly readmutat.[208]Page 134, line 22.Page 134, line 25.in rectâ sphærâ.—The meaning of the terms arightordirect sphere, anoblique sphereand aparallel sphereare explained by Moxon on pages 29 to 31 of his bookA Tutor to Astronomy and Geography(Lond., 1686):"ADirect Spherehath both thePolesof theWorldin the Horizon ... It is called aDirect Sphere, because all theCelestialBodies, asSun,Moon, andStars, &c. By theDiurnalMotion of thePrimum Mobile, ascend directly Above, and descend directly Below theHorizon. They that Inhabit under theEquatorhave theSpherethus posited.""AnOblique Spherehath theAxisof theWorldneitherDirectnorParallelto theHorizon, but lies aslope from it.""AParallel Spherehath onePoleof theWorldin theZenith, the other in theNadir, and theEquinoctialLine in theHorizon."[209]Page 136, line 1.Page 136, line 1.præsenti.—The editions of 1628 and 1633 readsequenti, to suit the altered position of the figure.[210]Page 137, line 24.Page 137, line 28.atque ille statim.—The Stettin editions both wrongly read illi.[211]Page 139.There is a curious history to this picture of the blacksmith in his smithy striking the iron while it lies north and south, and so magnetizing it under the influence of the earth's magnetism. Woodcuts containing human figures are comparatively rare in English art of the sixteenth century; a notable exception being Foxe'sActs and Monumentswith its many crude cuts of martyrdoms. The artist who prepared this cut of the smith took the design from an illustrated book of Fables by one Cornelius Kiliani or Cornelius van Kiel entitledViridarium Moralis Philosophiæ, per Fabulas Animalibus brutis attributas traditæ, etc.(Coloniæ, 1594). This rare work, of which there is no copy in the British Museum, is illustrated by some 120 fine copper-plate etchings printed in the text. On p. 133 of this work is an etching to illustrate the fableFerrarii fabri et canis, representing the smith smiting iron on the anvil, whilst his lazy dog sleeps beneath the bellows. The cut on p.139of Gilbert gives, as will be seen by a comparison of the pictures just the same general detail of forge and tools; but the position of the smith is reversed right for left, the dog is omitted, and the wordsSeptrenioandAusterhave been added.Source engraving.In the Stettin edition of 1628 the picture has again been turned into a copper-plate etching separately printed, is reversed back again left for right, while a compass-card is introduced in the corner to mark the north-south direction.In the Stettin edition of 1633 the artist has gone back to Kiliani's originalplate, and has re-etched the design very carefully, but reversing it all right for left. As in the London version of 1600, the dog is omitted, and the wordsSeptentrioandAusterare added. Some of the original details—for example, the vice and one pair of pincers—are left out, but other details, for instance, the cracks in the blocks that support the water-tub, and the dress of the blacksmith, are rendered with slavish fidelity.It is perhaps needless to remark that the twelve copper-plate etchings in the edition of 1628, and the twelve completely different ones in that of 1633, replace certain of the woodcuts of the folio of 1600. For example, take the woodcut on p.203of the 1600 edition, which represents a simple dipping-needle made by thrusting a versorium through a bit of cork and floating it, immersed, in a goblet of water. In the 1633 edition this appears, slightly reduced, as a small inserted copper-plate, with nothing added; but in the 1628 edition it is elaborated into a full-page plate (No. xi.) representing the interior, with shelves of books, of a library on the floor of which stands the goblet—apparently three feet high—with a globe and an armillary sphere; while beside the goblet, with his back to the spectator, is seated an aged man, reading, in a carved armchair. This figure and the view of the library are unquestionably copied—reversed—from a well-known plate in the workLe Diverse & Artificiose Machineof Agostino Ramelli (Paris, 1558).In the Emblems of Jacob Cats (Alle de Wercken, Amsterdam, 1665, p. 65) is given an engraved plate of a smith's forge, which is also copied—omitting the smith—from Kiliani'sViridarium.[212]Page 140, line 2.. Page 140, line 2.præcedenti.—This is so spelled in all editions, though the sense requirespræcedente.[213]Page 141, line 21.Page 141, line 24.quod in epistolâ quâdam Italicâ scribitur.—The tale told by Filippo Costa of Mantua about the magnetism acquired by the iron rod on the tower of the church of St. Augustine in Rimini is historical. The church was dedicated to St. John, but in the custody of the Augustinian monks. The following is the account of it given by Aldrovandi,Musæum Metallicum(1648, p. 134), on which page also two figures of it are given:"Aliquando etiam ferrum suam mutat substantiam, dum in magnetem conuertitur, & hoc experientia constat, nam Arimini supra turrim templi S. Ioannis erat Crux a baculo ferreo ponderis centum librarum sustentata, quod tractu temporis adeò naturam Magnetis est adeptum, vt, illivs instar, ferrum traheret: hinc magna admiratione multi tenentur, qua ratione ferrum, quod est metallum in Magnetem, qui est lapis transmutari possit; Animaduertendum est id à maxima familiaritate & sympathia ferri, & magnetis dimanare cum Aristoteles in habentibus symbolum facilem transitum semper admiserit. Hoc in loco damus imaginem frusti ferri in Magnetem transmutati, quod clarissimo viro Vlyssi Aldrouando Iulius Caesar Moderatus diligens rerum naturalium inquisitor communicauit; erat hoc frustum ferri colore nigro, & ferrugineo, crusta exteriori quodammodo albicante." And further on p. 557."Preterea id manifestissimum est; quoniam Arimini, in templo Sancti Ioannis, fuit Crux ferrea, quæ tractu temporis in magnetem conuersa est, & ab vno latere ferrum trahebat, & ab altero respuebat." See also Sir T. Browne'sPseudodoxia Epidemica(edition of 1650, p. 48), and Boyle's tract,Experiments and Notes about the Mechanical Production of Magnetism(London, 1676, p. 12).Another case is mentioned in Dr. Martin Lister'sA Journey to Paris(Lond., 1699, p. 83). "He [Mr. Butterfield] shewed us a Loadstone sawed off that piece of the Iron Bar which held the Stones together at the very top of the Steeple ofChartres. This was a thick Crust of Rust, part of which was turned into a strong Loadstone, and had all the properties of a Stone dug out of the Mine.Mons. de la Hirehas Printed a Memoir of it; also Mons.de Vallemonta Treatise. The very outward Rust had no Magnetic Virtue, but the inward had a strong one, as to take up a third part more than its weight unshod." Gassendi and Grimaldi have given other cases.Other examples of iron acquiring strong permanent magnetism from the earth are not wanting. The following is from Sir W. Snow Harris'sRudimentary Magnetism(London, 1872, p. 10)."In theMemoirs of the Academy of Sciencesfor 1731, we find an account of a large bell at Marseilles having an axis of iron: this axis rested on stone blocks, and threw off from time to time great quantities of rust, which, mixing with the particles of stone and the oil used to facilitate the motion, became conglomerated into a hardened mass: this mass had all the properties of the native magnet. The bell is supposed to have been in the same position for 400 years."[214]Page 142, line 13.Page 142, line 15.tunc planetæ & corpora cœlestia.—Gilbert's extraordinary detachment from all metaphysical and ultra-physical explanations of physical facts, and his continual appeal to the test of experimental evidence, enabled him to lift the science of the magnet out of the slough of the dark ages. This passage, however, reveals that he still gave credence to thenativitiesof judicial Astrology, and to the supposed influence of the planets on human destiny.[215]Page 144, line 14.Page 144, line 14.ijdem.—The editions of 1628 and 1633 erroneously readiisdem.[216]Page 147, line 27.Page 147, line 29.ex optimo aciario.—Gilbert recommended that the compass-needle should be of the best steel. Though the distinction between iron and steel was not at this time well established, there is no reason to doubt that byaciariumwas meant edge-steel as used for blades. Barlowe, in hisMagneticall Advertisements(Lond., 1616), p. 66, gives minute instructions for the fashioning of the compass-needle. He gives the preference to a pointed oval form, and describes how the steel must be hardened by heating to whiteness and quenching in water, so that it is "brickle in a manner as glass it selfe," and then be tempered by reheating it over a bar of red hot iron until it is let down to a blue tint. Savery (Philos. Trans., 1729) appears to have been the first to make a systematic examination of the magnetic differences between hard steel and soft iron.Instructions for touching the needle are given in theArte de Nauegarof Pedro de Medina (Valladolid, 1545, lib. vi., cap. 1).[217]Page 149, line 8.Page 149, line 9.per multa sæcula.—Compare Porta's assertion (p. 208, English edition) "iron once rubbed will hold the vertue a hundred years." Clearly not a matter within the actual experience of either Porta or Gilbert.[218]Page 153, line 2.Page 153, line 2.Cardani ab ortu stellæ in cauda vrsæ.—What Cardan said (De Subtilitate,Edit. citat., p. 187) was: "ortum stellæ in cauda ursæ minoris, quæ quinque partibus orientalior est polo mundi, respicit."[219]Page 153, line 21.Page 153, line 26.sequitur quod versus terram magnam, siue continentem ... à vero polo inclinatio magnetica fiat.—Gilbertgoes on to point out how, at that date, all the way up the west European coast from Morocco to Norway, the compass is deflected eastward, or toward the elevated land. He argued that this was a universal law.InPurchas his Pilgrimes(Lond., 1625), in the Narrative, in vol. iii., of Bylot and Baffin's Voyage of 1616, there is mentioned an island between Whale-Sound and Smith's Sound, where there had been observed a larger variation than in any other part of the world. Purchas, in a marginal note, comments on this as follows: "Variation of the Compass 56° to the West, which may make questionable D. Gilbert's rule, tom. 1., l. 2, c. 1, that where more Earth is more attraction of the Compass happeneth by variation towards it. Now the known Continents of Asia, &c., must be unspeakably more than here there can be, & yet here is more variation then about Jepan, Brasil, or Peru, &c."Gilbert's view was in truth founded on an incomplete set of facts. At that time, as he tells us, the variation of the compass at London was 11⅓ degrees eastward. But he did not know of the secular change which would in about fifty-seven years reduce that variation to zero. Still less did he imagine that there would then begin a westward variation which in the year 1816 should reach 24° 30', and which should then steadily diminish so that in the year 1900 it should stand at 16° 16' westward. For an early discussion of the changes of the variation see vol. i. of thePhilosophical Transactions(Abridged), p. 188. Still earlier is the classical volume of Henry Gellibrand,A Discovrse Mathematical on the Variation of the Magneticall Needle(Lond., 1635). Gilbert heads chapter iii. of book iiii. (p.159) with the assertionVariatio uniuscuiusque loci constans est, declaring that to change it would require the upheaval of a continent. Gellibrand combats this on p. 7 of the work mentioned. He says:"Thus hitherto (according to the Tenents of all ourMagneticallPhilosophers) we have supposed the variations of all particular places to continue one and the same. So that when a Seaman shall happly returne to a place where formerly he found the same variation, he may hence conclude he is in the same formerLongitude. For it is the Assertion ofMr. Dr. Gilberts.Variatio vnicuiusq; Loci constans est, that is to say, the same place doth alwayes retaine the same variation. Neither hath this Assertion (for ought I ever heard) been questioned by any man. But most diligent magneticall observations have plainely offred violence to the same, and proved the contrary, namely that the variation is accompanied with a variation."In 1637 Henry Bond wrote in theSea-Mans Kalendarthat in the year 1657 the variation would be zero at London. Compare Bond'sLongitude Found(Lond., 1676, p. 3).As to inconstancy of the variation in one place see further Fournier'sHydrographie(Paris, 1667, liv. xi., ch. 12, p. 413), and Kircher,Magnes(Colon. Agripp., 1643, p. 418).[220]Page 157, line 4.Page 157, line 5.perfecto.—Though this word is thus in all editions, it ought to standperfectâ, as in line10below.[221]Page 157, line 11.Page 157, line 13.varietas, forvariatio.[222]Page 160, line 20.Page 160, line 23.in Borrholybicum.—This name for the North-west, or North-North-West, is rarely used. It is found on the chart or windrose of the names of the winds on pp. 151 and 152 of theMécometrie de l'Eymanof G. Nautonier (1602). Here the nameBorrolybicusis given as a synonym forNortouest Galerne, orὈλυμπιάς, while the two winds on the points next on the western and northern sides respectively are calledUpocorusandUpocircius.In Swan'sSpecvlvm Mundi(Camb., 1643, p. 174) is this explanation: "Borrholybicus is the North-west wind."In Kircher'sMagnes(Colon. Agripp., 1643, p. 434) is a table of the names of the thirty-two winds in six languages, whereBorrolybicusis given as the equivalent ofMaestroorNorth-West.[223]Page 161, line 2.Page 161, line 2.Insula in Oceano variationem non mutat.—The conclusions derived from the magnetic explorations of the Challenger expedition, 1873-1876, are briefly these: That in islands north of the magnetic equator there is a tendency to produce a local perturbation, attracting the north-seeking end of the needle downwards, and horizontally towards the higher parts of the land; while south of the magnetic equator, the opposite effects are observed. (SeeChallenger Reports, Physics and Chemistry, vol. ii., part vi.,Report on the Magnetical Resultsby Staff-Commander Creak, F.R.S.)[224]Page 162, line 2.Page 162, line 3.quarè & respectiuum punctum ... excogitauit.—The passage referred to is inThe newe Attractiueof Robert Norman (Lond., 1581), chap. vi."Your reason towards the earth carrieth some probabilitie, but I prove that there be noAttractive, or drawing propertie in neyther of these two partes, then is theAttractivepoynt lost, and falsly called the poyntAttractive, as shall be proved. But because there is a certayne point that the Needle alwayes respecteth or sheweth, being voide and without anyAttractivepropertie: in my judgment this poynt ought rather to bee called the point Respective ... This PoyntRespective, is a certayne poynt, which the touched Needle doth alwayesRespector shew ..."[225]Page 165, line 2.Page 165, line 2.De pyxidis nauticæ vsitatæ compositione.—Gilbert's description of the usual construction of the mariner's compass should be compared with those given by Levinus Lemnius inThe Secret Miracles of Nature(London, 1658); by Lipenius inNavigatio Salomonis Ophiritica(Witteb., 1660, p. 333); and with that given in Barlowe'sNavigators Supply(London, 1597). See also Robert Dudley'sDell' Arcano del Mare(Firenze, 1646).[226]Page 165deals with the construction; the process of magnetizing by the loadstone had already been discussed in pp.147to149. It is interesting to see that already the magnetized part attached below the compass-card was being specialized in form, being made either of two pieces bent to meet at their ends, or of a single oval piece with elongated ends. The marking of the compass-card is particularly described. It was divided into thirty-two points or "winds," precisely as the earlier "wind-rose" of the geographers, distinguisht by certain marks, and by a lily—or fleur-de-lys—indicating the North. Stevin in theHavenfinding Art(London, 1599), from which work the passage on p.167is quoted, speaking on p. 20 of "the Instrument which we call the Sea-directorie, some the nautical box, ... or the sea compasse," mentions the "Floure de luce" marking the North.The legend which assigns the invention of the compass to one Goia or Gioja of Amalfi in 1302 has been already discussed in theNoteto page4. Gilbert generously says that in spite of the adverse evidence he does not wish to deprive the Amalfians of the honour of the construction adopted in the compasses used in the Mediterranean. But Baptista Porta the Neapolitan, who wrote forty years before Gilbert, discredited the legend. "Flaviussaith, an Italian found it out first, whose name wasAmalphus, born in ourCampania. But he knew not the Mariners Card, but stuck the needle in a reed, or a piece of wood, cross over; and he put the needles into a vessel full of water that they might flote freely." (Porta'sNatural Magick, English translation, London, 1658, p. 206.) See also Lipenius (op. citat.p. 390).The pivotting of the needle is expressly described in the famousEpistleon the Magnet of Peter Peregrinus, which was written in 1269. Gasser's edition,Epistola Petri Peregrini ... de magnete, was printed in Augsburg in 1558. In Part II., cap. 2, of this letter, a form of instrument is described for directing one's course to towns and islands, and any places in fact on land or sea. This instrument consists of a vessel like a turned box (orpyxis) of wood, brass, or any solid material, not deep, but sufficiently wide, provided with a cover of glass or crystal. In its middle is arranged a slender axis of brass or silver, pivotted at its two ends into the top and the bottom of the box. This axis is pierced orthogonally with two holes, through one of which is passed the steel needle, while through the other is fixed square across the needle another stylus of silver or brass. The glass cover was to be marked with two cross lines north-south and east-west; and each quadrant was to be divided into ninety degrees. This the earliest described pivotted compass was therefore of the cross-needle type, a form claimed as a new invention by Barlowe in 1597. The first suggestion of suspending a magnetic needle by a thread appears to be in theSpeculum Lapidumof Camillus Leonardus (Venet., 1502, fig. k ij, lines 25-31): "Nã tacto ferro ex unapte magnetis ex opposita eiuspte appropinquato fugat: ut expiẽtia docet de acu appenso filo."
1. The generalization of the class ofElectrics.2. The observation that damp weather hinders electrification.3. The generalization that electrified bodies attract everything,including even metals, water, and oil.4. The invention of the non-magneticversoriumor electroscope.5. The observation that merely warming amber does not electrify it.6. The recognition of a definite class ofnon-electrics.7. The observation that certain electrics do not attract if roasted orburnt.8. That certain electrics when softened by heat lose their power.9. That the electric effluvia are stopped by the interposition of a sheetof paper or a piece of linen, or by moist air blown from the mouth.10. That glowing bodies, such as a live coal, brought near excited amberdischarge its power.11. That the heat of the sun, even when concentrated by a burning mirror,confers no vigour on the amber, but dissipates the effluvia.12. That sulphur and shell-lac when aflame are not electric.13. That polish is not essential for an electric.14. That the electric attracts bodies themselves, not the intervening air.15. That flame is not attracted.16. That flame destroys the electrical effluvia.17. That during south winds and in damp weather, glass and crystal, whichcollect moisture on their surface, are electrically more interferedwith than amber, jet and sulphur, which do not so easily take upmoisture on their surfaces.18. That pure oil does not hinder production of electrification or exerciseof attraction.19. That smoke is electrically attracted, unless too rare.20. That the attraction by an electric is in a straight line toward it.
1. The generalization of the class ofElectrics.2. The observation that damp weather hinders electrification.3. The generalization that electrified bodies attract everything,including even metals, water, and oil.4. The invention of the non-magneticversoriumor electroscope.5. The observation that merely warming amber does not electrify it.6. The recognition of a definite class ofnon-electrics.7. The observation that certain electrics do not attract if roasted orburnt.8. That certain electrics when softened by heat lose their power.9. That the electric effluvia are stopped by the interposition of a sheetof paper or a piece of linen, or by moist air blown from the mouth.10. That glowing bodies, such as a live coal, brought near excited amberdischarge its power.11. That the heat of the sun, even when concentrated by a burning mirror,confers no vigour on the amber, but dissipates the effluvia.12. That sulphur and shell-lac when aflame are not electric.13. That polish is not essential for an electric.14. That the electric attracts bodies themselves, not the intervening air.15. That flame is not attracted.16. That flame destroys the electrical effluvia.17. That during south winds and in damp weather, glass and crystal, whichcollect moisture on their surface, are electrically more interferedwith than amber, jet and sulphur, which do not so easily take upmoisture on their surfaces.18. That pure oil does not hinder production of electrification or exerciseof attraction.19. That smoke is electrically attracted, unless too rare.20. That the attraction by an electric is in a straight line toward it.
1. The generalization of the class ofElectrics.
2. The observation that damp weather hinders electrification.
3. The generalization that electrified bodies attract everything,
including even metals, water, and oil.
4. The invention of the non-magneticversoriumor electroscope.
5. The observation that merely warming amber does not electrify it.
6. The recognition of a definite class ofnon-electrics.
7. The observation that certain electrics do not attract if roasted or
burnt.
8. That certain electrics when softened by heat lose their power.
9. That the electric effluvia are stopped by the interposition of a sheet
of paper or a piece of linen, or by moist air blown from the mouth.
10. That glowing bodies, such as a live coal, brought near excited amber
discharge its power.
11. That the heat of the sun, even when concentrated by a burning mirror,
confers no vigour on the amber, but dissipates the effluvia.
12. That sulphur and shell-lac when aflame are not electric.
13. That polish is not essential for an electric.
14. That the electric attracts bodies themselves, not the intervening air.
15. That flame is not attracted.
16. That flame destroys the electrical effluvia.
17. That during south winds and in damp weather, glass and crystal, which
collect moisture on their surface, are electrically more interfered
with than amber, jet and sulphur, which do not so easily take up
moisture on their surfaces.
18. That pure oil does not hinder production of electrification or exercise
of attraction.
19. That smoke is electrically attracted, unless too rare.
20. That the attraction by an electric is in a straight line toward it.
[128]Page 48, line 35.Page 48, line 39.quæ sunt illæ materiæ.—Gilbert's list of electrics should be compared with those given subsequently by Cabeus (1629), by Sir Thomas Browne (1646), and by Bacon. The last-named list occurs in hisPhysiological Remains, published posthumously in 1679; it contains nothing new. Sir Thomas Browne's list is given in the following passage, which is interesting as using for the first time in the English language the nounElectricities:
"Many stones also both precious and vulgar, although terse and smooth, have not this power attractive; as Emeralds, Pearle, Jaspis, Corneleans, Agathe, Heliotropes, Marble, Alablaster, Touchstone, Flint and Bezoar. Glasse attracts but weakely though cleere, some slick stones and thick glasses indifferently: Arsenic but weakely, so likewise glasse of Antimony, but Crocus Metallorum not at all. Saltes generally but weakely, as Sal Gemma, Alum, and also Talke, nor very discoverably by any frication: but if gently warmed at the fire, and wiped with a dry cloth, they will better discover their Electricities."(Pseudodoxia Epidemica, p. 79.)
In thePhilosophical Transactions, vol. xx., p. 384, isA Catalogue of Electrical Bodiesby the late Dr. Rob. Plot. It begins "Non solum succinum," and ends "alumen rupeum," being identical with Gilbert's list except that he calls "Vincentina & Bristolla" by the name "Pseudoadamas Bristoliensis."
[129]Page 49, line 25.Page 49, line 30.non dissimili modo.—Themodusoperandiof the electrical attractions was a subject of much discussion; see Cardan,op. citat.
[130]Page 51, line 2.Page 51, line 1.appellunt.—This appears to be a misprint forappelluntur.
[131]Page 51, line 22.Page 51, line 23.smyris.—Emery. This substance is mentioned on p.22as a magnetic body.
[132]Page 52, line 1.Page 51, line 46.gemmæ ... vt Crystallus, quæ ex limpidâ concreuit.See thenoteto p.48.
[133]Page 52, line 30.Page 52, line 32.ammoniacum.—Ammoniacum, or Gutta Ammoniaca, is described by Dioscorides as being the juice of a ferula grown in Africa, resembling galbanum, and used for incense.
"Ammoniackis a kind of Gum like Frankincense; it grows in Lybia, whereAmmon'sTemple was." Sir Hugh Plat'sJewel House of Art and Nature(Ed. 1653, p. 223).
[134]Page 52, line 38.Page 52, line 41.duæ propositæ sunt causæ ... materia & forma.—Gilbert had imbibed the schoolmen's ideas as to the relations of matter and form. He had discovered and noted that in the magnetic attractions there was always a verticity, and that in the electrical attractions the rubbed electrical body had no verticity. To account for these differences he drew the inference that since (as he had satisfied himself) the magnetic actions were due toform, that is to say to something immaterial—to an "imponderable" as in the subsequent age it was called—the electrical actions must necessarily be due tomatter. He therefore put forward his idea that a substance to be an electric must necessarily consist of a concreted humour which is partially resolved into an effluvium by attrition. His discoveries that electric actions would not pass through flame, whilst magnetic actions would, and that electric actions could be screened off by interposing the thinnest layer of fabric such as sarcenet, whilst magnetic actions would penetrate thick slabs of every material except iron only, doubtless confirmed him in attributing the electric forces to the presence of these effluvia. See also p.65. There arose a fashion, which lasted over a century, for ascribing to "humours," or "fluids," or "effluvia," physical effects which could not otherwise be accounted for. Boyle's tracts of the years 1673 and 1674 on "effluviums," their "determinate nature," their "strange subtilty," and their "great efficacy," are examples.
[135]Page 53, line 9.Page 53, line 11.Magnes vero....—This passage from line9to line24states very clearly the differences to be observed between the magnetical and the electrical attractions.
[136]Page 53, line 36.Page 53, line 41.succino calefacto.—Ed. 1633 readssuccinumin error.
[137]Page 54, line 9.Page 54, line 11.Plutarchus ... in quæstionibus Platonicis.—The following Latin version of the paragraph inQuæstio sextais taken from the bilingual edition publisht at Venice in 1552, p. 17verso, liber vii., cap. 7 (or,Quæstio Septimain Ed. Didot, p. 1230).
"Electrum uero quæ apposita sunt, nequaquàm trahit, quem admodum nec lapis ille, qui sideritis nuncupatur, nec quicquā à seipso ad ea quæ in propinquo sunt, extrinsecus assilit. Verum lapis magnes effluxiones quasdam tum graves, tum etiam spiritales emittit, quibus aer continuatus & iunctus repellitur. Is deinceps alium sibi proximum impellit, qui in orbem circum actus, atque ad inanem locum rediens, ui ferrum fecum rapit & trahit. At Electrum uim quandam flammæ similem & spiritalem continet, quam quidemtritu summæ partis, quo aperiuntur meatus, foras eijcit. Nam leuissima corpuscula & aridissima quæ propè sunt, sua tenuitate atque imbecillitate ad seipsum ducit & rapit, cum non sit adeo ualens, nec tantum habeat ponderis & momenti ad expellendam aeris copiam, ut maiora corpora more Magnetis superare possit & uincere."
[138]Page 54, line 16.Page 54, line 18.Gemma Vincentij rupis.—See thenoteto p.48supra, where the nameVincentinaoccurs.
[139]Page 54, line 30.Page 54, line 35.orobi.—The editions of 1628 and 1633 readoribi.
[140]Page 55, line 34.Page 55, line 42.in euacuati.—The editions of 1628 and 1633 readinevacuati.
[141]Page 58, line 21.Page 58, line 25.assurgentem vndam ... declinat ab F.—These words are wanting in the Stettin editions.
[142]Page 59, line 9.Page 59, line 9.fluore.—This word is conjectured to be a misprint forfluxubut it stands in all editions.
[143]Page 59, line 22.Page 59, line 25.Ruunt ad electria.—This appears to be a slip forelectrica, which is the reading of the editions of 1628 and 1633.
[144]Page 60, line 7.Page 60, line 9.tanqmateriales radij.—The suggestion here of materialraysas themodus operandiof electric forces seems to foreshadow the notion of electric lines of force.
[145]Page 60, line 10.Page 60, line 12.Differentia inter magnetica & electrica.—Though Gilbert was the first systematically to explore the differences that exist between the magnetic attraction of iron and the electric attraction of all light substances, the point had not passed unheeded, for we find St. Augustine, in theDe Civitate Dei, liber xxi., cap. 6, raising the question why the loadstone which attracts iron should refuse to move straws. The many analogies between electric and magnetic phenomena had led many experimenters to speculate on the possibility of some connexion between electricity and magnetism. See, for example, Tiberius Cavallo,A Treatise on Magnetism, London, 1787, p. 126. Also the three volumes of J. H. van Swinden,Receuil de Mémoires sur l'Analogie de Electricité et du Magnétisme, La Haye, 1784. Aepinus wrote a treatise on the subject, entitledDe Similitudine vis electricæ et magneticæ(Petropolis, 1758). This was, of course, long prior to the discovery, by Oersted, in 1820, of the real connexion between magnetism and the electric current.
[146]Page 60, line 25.Page 60, line 31.Coitionem dicimus, non attractionem.—See the remarks, at the outset of these Notes, on Gilbert's definitions of words.
[147]Page 60, line 33.Page 61, line 1.Orpheus in suis carminibus.—This passage is in the chapterΛιθικάof Orpheus, verses 301 to 327. SeeNoteto p.11, line19.
[148]Page 61, line 15.Page 61, line 19.Platonis in Timæo opinio.—The passage runs (edition Didot, vol. ii., p. 240, or Stephanus, p. 80, C.):
Καὶ δὴ καὶ τὰ τῶν ὑδάτων πάντα ῥεύματα ἔτι δὲ τὰ τῶν κεραυνῶν πτώματα καὶ τὰ θαυμαζόμενα ἠλέκτρων περὶ τῆς ἕλξεως καὶ τῶν Ἡρακλείων λίθων, πάντων τούτων ὁλκὴ μὲν οὐκ ἔστιν οὐδένι ποτε, τὸ δὲ κενὸν εἶναι μηδεν περιωθεῖν τε αὑτὰ ταῦτα εἰς ἄλληλα, τό τε διακρινόμενα καὶ συγκρινόμενα πρὸς τήν αὑτῶν διαμειβόμενα ἕδραν ἕκαστα ἰέναι πάντα, τούτοις τοῖς παθήμασι πρὸς ἄλληλα συμπλεχθεῖσι τεθαυματουργημένα τῷ κατὰ τρόπον ζητοῦντι φανήσεται.
[149]Page 61, Line 30.Page 61, line 38. The English version of the lines of Lucretius is from Busby's translation.
[150]Page 62, line 5.Page 62, line 7.Iohannes Costæus Laudensis.—Joannes Costa, of Lodi, edited Galen and Avicenna. He also wrote aDe universali stirpium Natura(Aug. Taurin., 1578).
[151]Page 63, line 3.Page 63, line 4.Cornelius Gemma 10. Cosmocrit.—This refers to the workDe Naturæ Divinis Characterismis ... Libri ii. Avctore D. Corn. Gemma(Antv., 1575, lib. i., cap. vii., p. 123).
"Certè vt à magnete insensiles radij ferrum ad se attrahunt, ab echineide paruo pisciculo sistuntur plena nauigia, à catoblepa spiritu non homines solùm, sed & alta serpentum genera interimuntur, & saxa dehiscunt."
See also Kircher'sMagneticum Naturæ Regnum(Amsterodami, 1667, p. 172), Sectio iv., cap. iii., De Magnete Navium, quæ Remora seu Echeneis dicitur. See the note to p.7, line21.
[152]Page 63, line 6.Page 63, line 7.Guilielmus Puteanus.—Puteanus (Du Puys) wrote a workDe Medicamentorum quomodocunque Purgantium Facultatibus, Libri ii. (Lugd., 1552), in which he talks vaguely about the substantial "form" of the magnet, and quotes Aristotle and Galen.
[153]Page 63, line 21.Page 63, line 25.Baptistæ Portæ.—The passage in the translation is quoted from the English version of 1658, pp. 191, 192.
[154]Page 64, line 4.Page 64, line 9.Eruditè magis Scaliger.—Gilbert pokes fun at Scaliger, whose "erudite" guess (that the motion of iron to the magnet was that of the offspring toward the parent) is to be found in his bookDe Subtilitate, ad Cardanum, Exercitatio CII. (Lutetiæ, 1557, p. 156bis).
[155]Page 64, line 7.Page 64, line 11.Diuus Thomas.—On p.3Gilbert had already spoken of St. Thomas Aquinas as a man of intellect who would have added more about the magnet had he been more conversant with experiments. The passage here quoted is from the middle of Liber vii. of his commentaries on thede Physicaof Aristotle,Expositio Diui Thome Aquinatis Doctoris Angelici super octo libros Physicorum Aristotelis, etc. (Venice, Giunta edition, 1539, p. 96verso, col. 2).
[156]Page 64, line 16.Page 64, line 24.Cardinalis etiam Cusanus.—Cardinal de Cusa (Nicolas Khrypffs) wrote a set of dialogues on Statics,Nicolai Cusani de staticis experimentis dialogus(1550), of which an English version appeared in London in 1650 with the title,The Idiot in four books; the first and second of wisdom, the third of the minde, the fourth of statick experiments. By the famous and learned C. Cusanus.In the fourth bookof statick Experiments, Or experiments of the Ballance, occurs (p. 186) the following:
"Orat.Tell me, if thou hast any device whereby the vertues of stones may be weighed."Id.I thinke the vertue of the Load-stone might be weighed, if putting some Iron in one scale, and a Load-stone in the other, untill the ballance were even, then taking away the Load-stone, and some other thing of the same weight being put into the scale, the Load-stone were holden over the Iron, so that that scale wou'd begin to rise; by reason of the Load-stones attraction of the Iron, then take out some of the weight of the other scale, untill the scale wherein the iron is, doe sinke againe to the æquilibrium, or equality still holding the Load-stone unmovable as it was; I beleeve that by weight of what was taken out of the contrary scale, one might come proportionably to the weight of the vertue or power of the Load-stone. And in like manner, the vertue of a Diamond, might be found hereby, becausethey say it hinders the Load-stone from drawing of Iron; and so other vertues of other stones, consideration, being alwayes had of the greatnesse of the bodyes, because in a greater body, there is a greater power and vertue."
"Orat.Tell me, if thou hast any device whereby the vertues of stones may be weighed.
"Id.I thinke the vertue of the Load-stone might be weighed, if putting some Iron in one scale, and a Load-stone in the other, untill the ballance were even, then taking away the Load-stone, and some other thing of the same weight being put into the scale, the Load-stone were holden over the Iron, so that that scale wou'd begin to rise; by reason of the Load-stones attraction of the Iron, then take out some of the weight of the other scale, untill the scale wherein the iron is, doe sinke againe to the æquilibrium, or equality still holding the Load-stone unmovable as it was; I beleeve that by weight of what was taken out of the contrary scale, one might come proportionably to the weight of the vertue or power of the Load-stone. And in like manner, the vertue of a Diamond, might be found hereby, becausethey say it hinders the Load-stone from drawing of Iron; and so other vertues of other stones, consideration, being alwayes had of the greatnesse of the bodyes, because in a greater body, there is a greater power and vertue."
In the 1588 edition of Baptista Porta'sMagiæ Naturalis Libri xx., in lib. vii., cap. xviii., occurs the description of the use of the balance to which Gilbert refers.
[157]Page 67, line 21.Page 67, line 22.aëris rigore.—All editions read thus, but the sense seems to requirefrigore.
[158]Page 67, line 27.Page 67, line 31.Fracastorius.—See hisDe Sympathia, lib. i., cap. 5 (Giunta edition, 1574, p. 60).
[159]Page 68, line 5.Page 68, line 6.Thaletis Milesij.—See thenoteto p.11, line26.
[160]Page 68, line 30.Page 68, line 35.Ità coitio magnetica actus est magnetis, & ferri, non actio vnius.—See the introductory remarks to these notes. There is a passage in Scaliger'sDe Subtilitate ad Cardanum(Exercitat. CII., cap. 5, p. 156op. citat.) which may be compared with Gilbert's for its use of Greek terms: "Nã cùm uita dicatur actus animæ, acceptus est abs te actus pro actione. Sed actus ille estἐντελέχεια, nõ autemἔργον. At Magnetis attractio estἔργον, non autẽἐντελέχεια." To which Gilbert retorts: "non actio unius, utriusqueἐντελέχεια; nonἔργον,συνεντελέχειαet conactus potius quam sympathia." He returns on p.70to the attack on Scaliger's metaphysical notions. There is a parallel passage in theEpitome Naturalis Scientiæof Daniel Sennert (Oxoniæ, 1664), in the chapterDe Motu.
[161]Page 71, line 4.Page 71, line 8.vt in 8. physicorum Themistius existimat.—SeeOmnia Themistii Opera(Aldine edition, 1533, p. 63), Book 8 of his Paraphrase on Aristotle'sPhysica.
[162]Page 71, line 9.Page 71, line 14.Quod verò Fracastorius.—Op. citat., lib. i., cap. 7, p. 62verso.
[163]Page 73, line 2.Page 73, line 2.si A borealis.—The editions of 1628 and 1633 omit the twelve words next following.
[164]Page 73, line 9.Page 73, line 11.ex minera.—Minerais not a recognized word, even in late Latin. It occurs again, p.97, line12.
[165]Page 77, line 2.Page 77, line 2.multo magis.—This is anà fortioriargument. It is interesting to find Gilbert comparing the velocity of propagation of magnetic forces in space with the velocity of light. The parallel is completed in line 13 by the consideration that as the rays of light require to fall upon an object in order that they may become visible, so the magnetic forces require a magnetic object in order to render their presence sensible.
[166]Page 78, line 14.Page 78, line 16.Orbem terrarum distinguunt.—The editions of 1628 and 1633 here add a figure of a globe marked with meridians and parallels of latitude, but with an erroneous versorium pointing to the south. These editions also both readexistentiamfor the wordexistentiumin line20.
[167]Page 83, line 5.Page 83, line 5.magnes longior maiora pondera ferri attollit.—Gilbert discovered the advantage, for an equal mass of loadstone, of an elongated shape. It is now well known that the specific amount of magnetism retained by elongated forms exceeds that in a short piece of the same material subjected to equal magnetizing forces.
[168]Page 83, line 24.Page 83, line 28.Non obstant crassa tabulata.—Gilbert has several times referred (e.g., on p.77) to the way in which magnetic forces penetrate solid bodies. The experimental investigation in this chapteris the more interesting because it shows that Gilbert clearly perceived the shielding action of iron to be due to iron conducting aside or diverting the magnetic forces.
[169]Page 85, line 26.Page 85, line 31.non conveniant.—The editions of 1628 and 1633 both readet conveniant.
[170]Page 86, line 3.Page 86, line 3.illud quod exhalat.—Literally,that which exhales, in the sense of that which escapes: but in modern English the verb exhale in the active voice is now not used of the substance that escapes, but is used of the thing which emits it. It must therefore be renderedthat which is exhaled(i.e., breathed out).
[171]Page 86, line 13.Page 86, line 15.Ita tota interposita moles terrestris.—Gilbert's notion that the gravitational force of the moon in producing the tides actsthroughthe substance of the earth may seem curiously expressed. But the underlying contention is essentially true to-day. The force of gravity is not cut off or screened off by the interposition of other masses. A recent investigation by Professor Poynting, F.R.S., has shown that so far as all evidence goes all bodies, even the densest, are transparent with respect to gravitational forces.
[172]Page 86, line 18.Page 86, line 20.Sed de æstus ratione aliàs.—There is no further discussion of the tides inDe Magnete. But a short account is to be found in Gilbert's posthumous workDe Mundo nostro Sublunari Philosophia nova(Amsterdam, Elzevir, 1651), in Lib. v., the part which in the manuscript was left in English, and was turned into Latin by his brother. It comprises about fifteen quarto pages, from Cap. X. to Cap. XIX. inclusive, beginning with a characteristic diatribe against Taisnier, Levinus Lemnius, and Scaliger. But in assigning causes he himself goes wide of the mark. Proceeding by a process of elimination he first shows that the moon's light cannot be the cause that impels the tides. "Luna," he says, "non radio, non lumine, maria impellit. quomodo igitur? Sane corporum conspiratione, acque (ut similitudine rem exponam) Magnetica attractione." This cryptic utterance he proceeds to explain by a diagram, and adds: "Quare Luna non tam attrahit mare, quàm humorem & spiritum subterraneum; nec plus resistit interposita terra, quàm mensa, aut quicquam aliud densum, aut crassum, magnetis viribus."
[173]Page 87, line 7.Page 87, line 9.armatura.—Here this means the cap or snout of iron with which the loadstone was armed. This is apparently the first use of the term in this sense.
In theDialogues of Galileo(p. 369 of Salusbury'sMathematical Collections, Dialogue iii.), Sagredus and Salviatus discuss the arming of the loadstone, and the increased lifting power conferred by adding an iron cap. Salviatus mentions a loadstone in the Florentine Academy which, unarmed, weighed six ounces, lifting only two ounces, but which when armed took up 160 ounces. Whereupon Galileo makes Salviatus say: "I extreamly praise, admire, and envy this Authour, for that a conceit so stupendious should come into his minde. ... I think him [i.e., Gilbert] moreover worthy of extraordinary applause for the many new and true Observations that he made, to the disgrace of so many fabulous Authours, that write not only what they do not know, but whatever they hear spoken by the foolish vulgar, never seeking to assure themselves of the same by experience, perhaps, because they are unwilling to diminish the bulk of their Books."
[174]Page 87, line 12.Page 87, line 15. The reference tolib.3 isa misprint forlib.2. It is corrected in the edition of 1633, but not in that of 1628.
[175]Page 87, line 17.Page 87, line 21.conactu.—The editions of 1628 and 1633 readconatu.
[176]Page 88, line 2.Page 88, line 3.Coitio verò non fortior.—This heading to chap. xix., taken with the seven lines that follow, and the contrast drawn betweenunitioandcoitio, throw much light on the fundamental sense attached by Gilbert to the termcoitio. It is here clearly used in the sense ofmutual tendency toward union. Note also the contrasted use in chap. xx. of the verbscohæreandadhære. Adhærence connotes a one-sided force (an impossibility in physics), cohærence a mutual force.
[177]Page 90, line 9.Page 90, line 9.nempè vt alter polus maius pondus arripiat.—This acute observation is even now not as well known as it ought to be. Only so recently as 1861 Siemens patented the device of fastening a mass of iron to one end of an electromagnet in order to increase the power of the other end. The fact, so far as it relates to permanent magnets was known to Servington Savery. SeePhilos. Transactions, 1729, p. 295.
[178]Page 92, line 3.Page 92, line 4.Suspendit in aëre ferrum Baptista Porta.—Porta's experiment is thus described (Natural Magick, London, 1658, p. 204): "Petrus Pellegrinussaith, he shewed in another work how that might be done: but that work is not to be found. Why I think it extream hard, I shall say afterwards. But I say it may be done, because I have now done it, to hold it fast by an invisible band, to hang in the air; onely so, that it be bound with a small thread beneath, that it may not rise higher: and then striving to catch hold of the stone above, it will hang in the air, and tremble and wag itself."
[179]Page 97, line 29.Page 97, line 33.Sed quæri potest ...—The question here raised by Gilbert is whether the lifting-power of magnets of equal quality is proportional to their weight. If a stone weighing a drachm will lift a drachm, would a stone that weighs an ounce lift an ounce? Gilbert erroneously answers that this is so, and that the lifting-power of a loadstone, whether armed or unarmed, is proportional to its mass.
The true law of the tractive force or lifting-power of magnets was first given in 1729 by James Hamilton (afterwards Earl of Abercorn) in a work entitledCalculations and Tables Relating to the Attractive Virtue of Loadstones ... Printed[at London?]in the Year1729. (See also a paper in thePhilos. Transactions, 1729-30, vol. xxxvi., p. 245). This work begins thus:
"The Principle upon which these Tables are formed, is this: That if TwoLoadstonesare perfectly Homogeneous, that is, if their Matter be of the same Specifick Gravity, and of the same Virtue in all Parts of one Stone, as in the other; and that Like Parts of their Surfaces are Cap'd or Arm'd with Iron; then the Weights they sustain will be as the Squares of the Cube Roots of the Weights of theLoadstones; that is, as their Surfaces."
Upon lifting-power see also D. Bernoulli,Acta Helvetica, iii., p. 223, 1758; P. W. Haecker,Zur Theorie des Magnetismus, Nürnberg, 1856; Van der Willigen,Arch. du Musée Teyler, vol. iv., Haarlem, 1878 ; S. P. Thompson,Philos. Magazine, July, 1888.
In the book of James Hamilton, p. 5, he mentions a small terrella weighing 139 English grains, which would sustain no less than 23,760 grains, and was valued at £21 13s.10¾d.
In theMusæum Septalianumof Terzagus (Dertonæ, 1664, p. 42) is mentioned a loadstone weighing twelve ounces which would lift sixty pounds of iron.
Sir Isaac Newton had a loadstone weighing 3 grains, which he wore in a ring. It would lift 746 grains.
Thomson'sBritish Annual, 1837, p. 354, gives the following reference: "In theRecords of General Science, vol. iii., p. 272, there is an interesting description of a very powerful magnet which was sent from Virginia in 1776 by the celebrated Dr. Franklin to Professor Anderson, of Glasgow. It is now in the possession of Mr. Crichton. It weighs 2½ grains, and is capable of supporting a load of 783 grains, which is equivalent to 313 times its own weight."
[180]Page 99, line 10.Page 99, line 11.Manifestum est.—In this, as in many other passages, Gilbert uses this expression in the sense thatit is demonstrablerather than meaning thatit is obvious: for the fact here described is one that is not at all self-evident, but one which would become plain when the experiment had been tried. For other instances of this use ofmanifestumsee pages144, line20;158, line19;162, line10.
[181]Page 100, line 20.Page 100, line 24.si per impedimēta ... pervenire possunt.—All editions agree in this reading, but the sense undoubtedly requiresnon possint. Compare p.91, line21.
[182]Page 102, line 4.Page 102, line 4.capite4.—This is a misprint forcapite40, and is retained in the later editions. In the quotation from Baptista Porta, where the English version of 1658 is adhæred to, the words "& deturbat eam" have been omitted by the translator.
[183]Page 107, line 16.Page 107, line 18.Cardanus scribit.—The alleged perpetual motion machine is mentioned inDe rerum varietate,lib.9, cap. xlviii. (Basil., 1581, p. 641). See also theNoteto p.223. For Peregrinus and for Taisnier, see thenoteto p.5, lines8and12.
[184]Page 107, line 19.Page 107, line 21.Antonij de Fantis.—His work is:Tabula generalis scotice subtilitatis octo Sectionibus vniuersam Doctoris Subtilis Peritiā cōplectēs: ab excellentissimo doctore Antonio de Fātis taruisino edita ...Lugd., 1530.
[185]Page 108, line 26.Page 108, line 31.Cusani in staticis.—See thenoteto p.64, line16.
[186]Page 108, line 33.Page 108, line 41.Languidi ... tardiùs acquiescunt.—The editions of 1628 and 1633 omit these seven words.
[187]Page 109, line 11.Page 109, line 13.halinitro.—Either native carbonate of soda or native carbonate of potash might be meant, but not saltpetre. Scaliger, in hisDe Subtilitate ad Cardanum(Lutet., 1557, p. 164),ExercitatioCIII., 15, under the title,Nitrum non est Salpetræ, says: "More tuo te, tuaque confundis. Salpetræ inter salis fossilis ponis hîc. Mox Halinitrum inter salis, & nitri naturam, speciem obtinere."
"Sal nitrumis salt which is boiled out of the earth, especially fat earth, as in stables, or any place of excrements." (A Chymicall Dictionary explaining Hard Places and Words met withall in the Writings of Paracelsus ..., Lond., 1650.)
[188]Page 109, line 20.Page 109, line 23.arte ioculatoriâ.—Edition 1628,joculatoriâ; edition 1633,jaculatoriâ.
[189]Page 110, line 11.Page 110, line 12.qualis fuit Antonij denarius.—The Elizabethan version of Pliny (book xxxiii., ch. ix., p. 479) runs thus:"To come now unto those that counterfeit money.Antoniuswhiles hee was one of the three usurping Triumvirs, mixed yron with the Romane silver denier. He tempered it also with the brasen coine, and so sent abroad false and counterfeit money."
Georgius Agricola (De Natura Fossilium, p. 646) says:
"Sed ea fraus capitalis est, non aliter ac eorum qui adulterinas monetas cudunt, argento miscentes multam plumbi candidi portionem, aut etiam ferri, qualis fuit Antonii denarius, ut Plinius memoriæ tradidit. Nunc dicam de candido plumbo, nam majoris pretii est quàm aes. In quod plumbum album, inquit Plinius, addita aeris tertia portione candidi adulteratur stannum."
[190]Page 111, line 3.Page 111, line 3.Meminerunt Chatochitis lapis Plinius, atque Iulius Solinus.—The passage in Pliny (English version of 1601, book xxxvii., ch. x., p. 625) runs:
"Catochitis is a stone proper unto the Island Corsica: in bignesse it exceedeth ordinarie pretious stones: a wonderfull stone, if all be true that is reported thereof, and namely, That if a man lay his hand thereon, it will hold it fast in manner of a glewie gum."
[191]Page 111, line 7.Page 111, line 7.Sagda vel Sagdo.—Albertus Magnus inDe Mineralibus(Venet., 1542, p. 202) says:
"Sarda quem alij dicunt Sardo lapis est qui se habet ad tabulas ligni sicut magnes ad ferrū, et ideo adhæret ita fortiter tabulis nauium quòd euelli nō possit, nisi abscindatur cum ipso ea pars tabulæ cui inhæserit, est autē in colore purissimus nitens."
And Pliny (op. citat., p. 629):
"Sagda is a stone, which the Chaldeans find sticking to ships, and they say it is greene as Porrets or Leekes."
[192]Page 111, line 8.Page 111, line 8.Euace.—Evax, king of the Arabs, is said to have written to Nero a treatise on the names, colours, and properties of stones. See thenoteon Marbodæus, p.7, line20.
[193]Page 113, line 14.Page 113, line 19.repulsus sit.The words read thus in all editions, but the sense requiresrepulsa sint.
[194]Page 113, line 23.Page 113, line 29.Electrica omnia alliciunt cuncta, nihil omninò fugant vnquam, aut propellunt.This denial of electrical repulsion probably arose from the smallness of the pieces of electric material with which Gilbert worked. He could hardly have failed to notice it had he used large pieces of amber or of sealing-wax. Electrical repulsion was first observed by Nicolas Cabeus,Philosophia Magnetica, Ferrara, 1629; but first systematically announced by Otto von Guericke in his treatiseExperimenta Nova (ut vocantur) Magdeburgica, de Vacuo Spatio(Amstel., 1672).
[195]Page 113, line 29.Page 113, line 37.cùm de calore quid sit disputabimus.—The discussion of the nature of heat is to be found in Gilbert'sDe Mundo nostro Sublunari(Amstel., 1651), lib. i., cap. xxvi., pp. 77-88.
[196]Page 115, line 23.Page 115, line 23.trium vel quatuor digitorum.—Here as in all other places in Gilbert,digitusmeans a finger's breadth, so that three or four digits means a length of two or three inches, or from six to eight centimetres.
[197]Page 117, line 26.Page 117, line 25.ille Thebit Bencoræ trepidationis motus.
"Trepidation in the ancient Astronomy denotes a motion which in the Ptolemaic system was attributed to the firmament, in order to account forseveral changes and motions observed in the axis of the world, and for which they could not account on any other principle." (Barlow'sMathematical Dictionary.)
[198]Page 118, line 10.Page 118, line 8.cuspis is aut lilium.—Gilbert usescuspisorliliumalways of the North-pointing end of the needle. Sir Thomas Browne speaks of "the lilly or northern point"; but he differs from Gilbert in saying "thecuspisor Southern point" (Pseudodoxia Epidemica, 1650, p. 46). Only in one place (p.101, line5) does Gilbert speak ofcuspis meridionalis. Everywhere else the south-pointing end is called thecrux.
[199]Page 118, line 15.Page 118, line 13.nam æquè potens est.—Later observation showed this view to be incorrect. The horizontal component of the earth's magnetic field is not equally strong all over the globe, and the sluggishness of the needle's return to its position of rest is not due to the supporting pin becoming blunt with wear. The value of the horizontal component is zero at the north magnetic pole, and increases toward the magnetic equator. It is greatest near Singapore and in Borneo, being there more than twice as great as it is at London. (See Captain Creak inReport of Voyage of H.M.S. Challenger, Physics and Chemistry, vol. ii., part vi., 1889.)
[200]Page 119, line 5.Page 119, line 2.lapis.—Both Stettin editions readlapidis.
[201]Page 119, lines 9-11.Page 119, lines 7-9. The gist of the whole book is summarized in these lines. They furnish a cardinal example of that inductive reasoning which was practist by Gilbert, and of which Bacon subsequently posed as the apostle. Compare pages41and211.
[202]Page 120, line 8.Page 120, line 5.dicturi sumus.—Change of verticity is treated of in book iii., chap. x., pp.137to140.
[203]Page 125, line 24.Page 125, line 29.appositam.—All editions give this word, though the sense requiresappositum.
[204]Page 128, line 9.Page 128, line 11.non nimis longum.—The editions of 1628 and 1633 read (wrongly)minusinstead ofnimis.
[205]Page 130, line 12.Page 130, line 14. The wordhuncin the folio of 1600 is corrected in ink totunc, and the Stettin editions both readtunc.
[206]Page 132, line 9.Page 132, line 10.minimus & nullius ponderis.—The editions of 1628 and 1633 both wrongly readestfor&.
[207]Page 132, line 28.Page 133, line 1.nutat.—The editions of 1628 and 1633 both wrongly readmutat.
[208]Page 134, line 22.Page 134, line 25.in rectâ sphærâ.—The meaning of the terms arightordirect sphere, anoblique sphereand aparallel sphereare explained by Moxon on pages 29 to 31 of his bookA Tutor to Astronomy and Geography(Lond., 1686):
"ADirect Spherehath both thePolesof theWorldin the Horizon ... It is called aDirect Sphere, because all theCelestialBodies, asSun,Moon, andStars, &c. By theDiurnalMotion of thePrimum Mobile, ascend directly Above, and descend directly Below theHorizon. They that Inhabit under theEquatorhave theSpherethus posited."
"AnOblique Spherehath theAxisof theWorldneitherDirectnorParallelto theHorizon, but lies aslope from it."
"AParallel Spherehath onePoleof theWorldin theZenith, the other in theNadir, and theEquinoctialLine in theHorizon."
[209]Page 136, line 1.Page 136, line 1.præsenti.—The editions of 1628 and 1633 readsequenti, to suit the altered position of the figure.
[210]Page 137, line 24.Page 137, line 28.atque ille statim.—The Stettin editions both wrongly read illi.
[211]Page 139.There is a curious history to this picture of the blacksmith in his smithy striking the iron while it lies north and south, and so magnetizing it under the influence of the earth's magnetism. Woodcuts containing human figures are comparatively rare in English art of the sixteenth century; a notable exception being Foxe'sActs and Monumentswith its many crude cuts of martyrdoms. The artist who prepared this cut of the smith took the design from an illustrated book of Fables by one Cornelius Kiliani or Cornelius van Kiel entitledViridarium Moralis Philosophiæ, per Fabulas Animalibus brutis attributas traditæ, etc.(Coloniæ, 1594). This rare work, of which there is no copy in the British Museum, is illustrated by some 120 fine copper-plate etchings printed in the text. On p. 133 of this work is an etching to illustrate the fableFerrarii fabri et canis, representing the smith smiting iron on the anvil, whilst his lazy dog sleeps beneath the bellows. The cut on p.139of Gilbert gives, as will be seen by a comparison of the pictures just the same general detail of forge and tools; but the position of the smith is reversed right for left, the dog is omitted, and the wordsSeptrenioandAusterhave been added.
Source engraving.
In the Stettin edition of 1628 the picture has again been turned into a copper-plate etching separately printed, is reversed back again left for right, while a compass-card is introduced in the corner to mark the north-south direction.
In the Stettin edition of 1633 the artist has gone back to Kiliani's originalplate, and has re-etched the design very carefully, but reversing it all right for left. As in the London version of 1600, the dog is omitted, and the wordsSeptentrioandAusterare added. Some of the original details—for example, the vice and one pair of pincers—are left out, but other details, for instance, the cracks in the blocks that support the water-tub, and the dress of the blacksmith, are rendered with slavish fidelity.
It is perhaps needless to remark that the twelve copper-plate etchings in the edition of 1628, and the twelve completely different ones in that of 1633, replace certain of the woodcuts of the folio of 1600. For example, take the woodcut on p.203of the 1600 edition, which represents a simple dipping-needle made by thrusting a versorium through a bit of cork and floating it, immersed, in a goblet of water. In the 1633 edition this appears, slightly reduced, as a small inserted copper-plate, with nothing added; but in the 1628 edition it is elaborated into a full-page plate (No. xi.) representing the interior, with shelves of books, of a library on the floor of which stands the goblet—apparently three feet high—with a globe and an armillary sphere; while beside the goblet, with his back to the spectator, is seated an aged man, reading, in a carved armchair. This figure and the view of the library are unquestionably copied—reversed—from a well-known plate in the workLe Diverse & Artificiose Machineof Agostino Ramelli (Paris, 1558).
In the Emblems of Jacob Cats (Alle de Wercken, Amsterdam, 1665, p. 65) is given an engraved plate of a smith's forge, which is also copied—omitting the smith—from Kiliani'sViridarium.
[212]Page 140, line 2.. Page 140, line 2.præcedenti.—This is so spelled in all editions, though the sense requirespræcedente.
[213]Page 141, line 21.Page 141, line 24.quod in epistolâ quâdam Italicâ scribitur.—The tale told by Filippo Costa of Mantua about the magnetism acquired by the iron rod on the tower of the church of St. Augustine in Rimini is historical. The church was dedicated to St. John, but in the custody of the Augustinian monks. The following is the account of it given by Aldrovandi,Musæum Metallicum(1648, p. 134), on which page also two figures of it are given:
"Aliquando etiam ferrum suam mutat substantiam, dum in magnetem conuertitur, & hoc experientia constat, nam Arimini supra turrim templi S. Ioannis erat Crux a baculo ferreo ponderis centum librarum sustentata, quod tractu temporis adeò naturam Magnetis est adeptum, vt, illivs instar, ferrum traheret: hinc magna admiratione multi tenentur, qua ratione ferrum, quod est metallum in Magnetem, qui est lapis transmutari possit; Animaduertendum est id à maxima familiaritate & sympathia ferri, & magnetis dimanare cum Aristoteles in habentibus symbolum facilem transitum semper admiserit. Hoc in loco damus imaginem frusti ferri in Magnetem transmutati, quod clarissimo viro Vlyssi Aldrouando Iulius Caesar Moderatus diligens rerum naturalium inquisitor communicauit; erat hoc frustum ferri colore nigro, & ferrugineo, crusta exteriori quodammodo albicante." And further on p. 557.
"Preterea id manifestissimum est; quoniam Arimini, in templo Sancti Ioannis, fuit Crux ferrea, quæ tractu temporis in magnetem conuersa est, & ab vno latere ferrum trahebat, & ab altero respuebat." See also Sir T. Browne'sPseudodoxia Epidemica(edition of 1650, p. 48), and Boyle's tract,Experiments and Notes about the Mechanical Production of Magnetism(London, 1676, p. 12).
Another case is mentioned in Dr. Martin Lister'sA Journey to Paris(Lond., 1699, p. 83). "He [Mr. Butterfield] shewed us a Loadstone sawed off that piece of the Iron Bar which held the Stones together at the very top of the Steeple ofChartres. This was a thick Crust of Rust, part of which was turned into a strong Loadstone, and had all the properties of a Stone dug out of the Mine.Mons. de la Hirehas Printed a Memoir of it; also Mons.de Vallemonta Treatise. The very outward Rust had no Magnetic Virtue, but the inward had a strong one, as to take up a third part more than its weight unshod." Gassendi and Grimaldi have given other cases.
Other examples of iron acquiring strong permanent magnetism from the earth are not wanting. The following is from Sir W. Snow Harris'sRudimentary Magnetism(London, 1872, p. 10).
"In theMemoirs of the Academy of Sciencesfor 1731, we find an account of a large bell at Marseilles having an axis of iron: this axis rested on stone blocks, and threw off from time to time great quantities of rust, which, mixing with the particles of stone and the oil used to facilitate the motion, became conglomerated into a hardened mass: this mass had all the properties of the native magnet. The bell is supposed to have been in the same position for 400 years."
[214]Page 142, line 13.Page 142, line 15.tunc planetæ & corpora cœlestia.—Gilbert's extraordinary detachment from all metaphysical and ultra-physical explanations of physical facts, and his continual appeal to the test of experimental evidence, enabled him to lift the science of the magnet out of the slough of the dark ages. This passage, however, reveals that he still gave credence to thenativitiesof judicial Astrology, and to the supposed influence of the planets on human destiny.
[215]Page 144, line 14.Page 144, line 14.ijdem.—The editions of 1628 and 1633 erroneously readiisdem.
[216]Page 147, line 27.Page 147, line 29.ex optimo aciario.—Gilbert recommended that the compass-needle should be of the best steel. Though the distinction between iron and steel was not at this time well established, there is no reason to doubt that byaciariumwas meant edge-steel as used for blades. Barlowe, in hisMagneticall Advertisements(Lond., 1616), p. 66, gives minute instructions for the fashioning of the compass-needle. He gives the preference to a pointed oval form, and describes how the steel must be hardened by heating to whiteness and quenching in water, so that it is "brickle in a manner as glass it selfe," and then be tempered by reheating it over a bar of red hot iron until it is let down to a blue tint. Savery (Philos. Trans., 1729) appears to have been the first to make a systematic examination of the magnetic differences between hard steel and soft iron.
Instructions for touching the needle are given in theArte de Nauegarof Pedro de Medina (Valladolid, 1545, lib. vi., cap. 1).
[217]Page 149, line 8.Page 149, line 9.per multa sæcula.—Compare Porta's assertion (p. 208, English edition) "iron once rubbed will hold the vertue a hundred years." Clearly not a matter within the actual experience of either Porta or Gilbert.
[218]Page 153, line 2.Page 153, line 2.Cardani ab ortu stellæ in cauda vrsæ.—What Cardan said (De Subtilitate,Edit. citat., p. 187) was: "ortum stellæ in cauda ursæ minoris, quæ quinque partibus orientalior est polo mundi, respicit."
[219]Page 153, line 21.Page 153, line 26.sequitur quod versus terram magnam, siue continentem ... à vero polo inclinatio magnetica fiat.—Gilbertgoes on to point out how, at that date, all the way up the west European coast from Morocco to Norway, the compass is deflected eastward, or toward the elevated land. He argued that this was a universal law.
InPurchas his Pilgrimes(Lond., 1625), in the Narrative, in vol. iii., of Bylot and Baffin's Voyage of 1616, there is mentioned an island between Whale-Sound and Smith's Sound, where there had been observed a larger variation than in any other part of the world. Purchas, in a marginal note, comments on this as follows: "Variation of the Compass 56° to the West, which may make questionable D. Gilbert's rule, tom. 1., l. 2, c. 1, that where more Earth is more attraction of the Compass happeneth by variation towards it. Now the known Continents of Asia, &c., must be unspeakably more than here there can be, & yet here is more variation then about Jepan, Brasil, or Peru, &c."
Gilbert's view was in truth founded on an incomplete set of facts. At that time, as he tells us, the variation of the compass at London was 11⅓ degrees eastward. But he did not know of the secular change which would in about fifty-seven years reduce that variation to zero. Still less did he imagine that there would then begin a westward variation which in the year 1816 should reach 24° 30', and which should then steadily diminish so that in the year 1900 it should stand at 16° 16' westward. For an early discussion of the changes of the variation see vol. i. of thePhilosophical Transactions(Abridged), p. 188. Still earlier is the classical volume of Henry Gellibrand,A Discovrse Mathematical on the Variation of the Magneticall Needle(Lond., 1635). Gilbert heads chapter iii. of book iiii. (p.159) with the assertionVariatio uniuscuiusque loci constans est, declaring that to change it would require the upheaval of a continent. Gellibrand combats this on p. 7 of the work mentioned. He says:
"Thus hitherto (according to the Tenents of all ourMagneticallPhilosophers) we have supposed the variations of all particular places to continue one and the same. So that when a Seaman shall happly returne to a place where formerly he found the same variation, he may hence conclude he is in the same formerLongitude. For it is the Assertion ofMr. Dr. Gilberts.Variatio vnicuiusq; Loci constans est, that is to say, the same place doth alwayes retaine the same variation. Neither hath this Assertion (for ought I ever heard) been questioned by any man. But most diligent magneticall observations have plainely offred violence to the same, and proved the contrary, namely that the variation is accompanied with a variation."
"Thus hitherto (according to the Tenents of all ourMagneticallPhilosophers) we have supposed the variations of all particular places to continue one and the same. So that when a Seaman shall happly returne to a place where formerly he found the same variation, he may hence conclude he is in the same formerLongitude. For it is the Assertion ofMr. Dr. Gilberts.Variatio vnicuiusq; Loci constans est, that is to say, the same place doth alwayes retaine the same variation. Neither hath this Assertion (for ought I ever heard) been questioned by any man. But most diligent magneticall observations have plainely offred violence to the same, and proved the contrary, namely that the variation is accompanied with a variation."
In 1637 Henry Bond wrote in theSea-Mans Kalendarthat in the year 1657 the variation would be zero at London. Compare Bond'sLongitude Found(Lond., 1676, p. 3).
As to inconstancy of the variation in one place see further Fournier'sHydrographie(Paris, 1667, liv. xi., ch. 12, p. 413), and Kircher,Magnes(Colon. Agripp., 1643, p. 418).
[220]Page 157, line 4.Page 157, line 5.perfecto.—Though this word is thus in all editions, it ought to standperfectâ, as in line10below.
[221]Page 157, line 11.Page 157, line 13.varietas, forvariatio.
[222]Page 160, line 20.Page 160, line 23.in Borrholybicum.—This name for the North-west, or North-North-West, is rarely used. It is found on the chart or windrose of the names of the winds on pp. 151 and 152 of theMécometrie de l'Eymanof G. Nautonier (1602). Here the nameBorrolybicusis given as a synonym forNortouest Galerne, orὈλυμπιάς, while the two winds on the points next on the western and northern sides respectively are calledUpocorusandUpocircius.
In Swan'sSpecvlvm Mundi(Camb., 1643, p. 174) is this explanation: "Borrholybicus is the North-west wind."
In Kircher'sMagnes(Colon. Agripp., 1643, p. 434) is a table of the names of the thirty-two winds in six languages, whereBorrolybicusis given as the equivalent ofMaestroorNorth-West.
[223]Page 161, line 2.Page 161, line 2.Insula in Oceano variationem non mutat.—The conclusions derived from the magnetic explorations of the Challenger expedition, 1873-1876, are briefly these: That in islands north of the magnetic equator there is a tendency to produce a local perturbation, attracting the north-seeking end of the needle downwards, and horizontally towards the higher parts of the land; while south of the magnetic equator, the opposite effects are observed. (SeeChallenger Reports, Physics and Chemistry, vol. ii., part vi.,Report on the Magnetical Resultsby Staff-Commander Creak, F.R.S.)
[224]Page 162, line 2.Page 162, line 3.quarè & respectiuum punctum ... excogitauit.—The passage referred to is inThe newe Attractiueof Robert Norman (Lond., 1581), chap. vi.
"Your reason towards the earth carrieth some probabilitie, but I prove that there be noAttractive, or drawing propertie in neyther of these two partes, then is theAttractivepoynt lost, and falsly called the poyntAttractive, as shall be proved. But because there is a certayne point that the Needle alwayes respecteth or sheweth, being voide and without anyAttractivepropertie: in my judgment this poynt ought rather to bee called the point Respective ... This PoyntRespective, is a certayne poynt, which the touched Needle doth alwayesRespector shew ..."
[225]Page 165, line 2.Page 165, line 2.De pyxidis nauticæ vsitatæ compositione.—Gilbert's description of the usual construction of the mariner's compass should be compared with those given by Levinus Lemnius inThe Secret Miracles of Nature(London, 1658); by Lipenius inNavigatio Salomonis Ophiritica(Witteb., 1660, p. 333); and with that given in Barlowe'sNavigators Supply(London, 1597). See also Robert Dudley'sDell' Arcano del Mare(Firenze, 1646).
[226]Page 165deals with the construction; the process of magnetizing by the loadstone had already been discussed in pp.147to149. It is interesting to see that already the magnetized part attached below the compass-card was being specialized in form, being made either of two pieces bent to meet at their ends, or of a single oval piece with elongated ends. The marking of the compass-card is particularly described. It was divided into thirty-two points or "winds," precisely as the earlier "wind-rose" of the geographers, distinguisht by certain marks, and by a lily—or fleur-de-lys—indicating the North. Stevin in theHavenfinding Art(London, 1599), from which work the passage on p.167is quoted, speaking on p. 20 of "the Instrument which we call the Sea-directorie, some the nautical box, ... or the sea compasse," mentions the "Floure de luce" marking the North.
The legend which assigns the invention of the compass to one Goia or Gioja of Amalfi in 1302 has been already discussed in theNoteto page4. Gilbert generously says that in spite of the adverse evidence he does not wish to deprive the Amalfians of the honour of the construction adopted in the compasses used in the Mediterranean. But Baptista Porta the Neapolitan, who wrote forty years before Gilbert, discredited the legend. "Flaviussaith, an Italian found it out first, whose name wasAmalphus, born in ourCampania. But he knew not the Mariners Card, but stuck the needle in a reed, or a piece of wood, cross over; and he put the needles into a vessel full of water that they might flote freely." (Porta'sNatural Magick, English translation, London, 1658, p. 206.) See also Lipenius (op. citat.p. 390).
The pivotting of the needle is expressly described in the famousEpistleon the Magnet of Peter Peregrinus, which was written in 1269. Gasser's edition,Epistola Petri Peregrini ... de magnete, was printed in Augsburg in 1558. In Part II., cap. 2, of this letter, a form of instrument is described for directing one's course to towns and islands, and any places in fact on land or sea. This instrument consists of a vessel like a turned box (orpyxis) of wood, brass, or any solid material, not deep, but sufficiently wide, provided with a cover of glass or crystal. In its middle is arranged a slender axis of brass or silver, pivotted at its two ends into the top and the bottom of the box. This axis is pierced orthogonally with two holes, through one of which is passed the steel needle, while through the other is fixed square across the needle another stylus of silver or brass. The glass cover was to be marked with two cross lines north-south and east-west; and each quadrant was to be divided into ninety degrees. This the earliest described pivotted compass was therefore of the cross-needle type, a form claimed as a new invention by Barlowe in 1597. The first suggestion of suspending a magnetic needle by a thread appears to be in theSpeculum Lapidumof Camillus Leonardus (Venet., 1502, fig. k ij, lines 25-31): "Nã tacto ferro ex unapte magnetis ex opposita eiuspte appropinquato fugat: ut expiẽtia docet de acu appenso filo."