[206] PAGE 132, LINE 9. Page 132, line 10. _minimus & nullius ponderis._--The editions of 1628 and 1633 both wrongly read _est_ for _&_.

[207] PAGE 132, LINE 28. Page 133, line 1. _nutat._--The editions of 1628 and 1633 both wrongly read _mutat_.

[208] PAGE 134, LINE 22. Page 134, line 25. _in recta sphaera._--The meaning of the terms a _right_ or _direct sphere_, an _oblique sphere_ and a _parallel sphere_ are explained by Moxon on pages 29 to 31 of his book _A Tutor to Astronomy and Geography_ (Lond., 1686):

"A _Direct Sphere_ hath both the _Poles_ of the _World_ in the Horizon ...

It is called a _Direct Sphere_, because all the _Celestial_ Bodies, as _Sun_, _Moon_, and _Stars_, &c. By the _Diurnal_ Motion of the _Primum Mobile_, ascend directly Above, and descend directly Below the _Horizon_.

They that Inhabit under the _Equator_ have the _Sphere_ thus posited."

"An _Oblique Sphere_ hath the _Axis_ of the _World_ neither _Direct_ nor _Parallel_ to the _Horizon_, but lies aslope from it."

"A _Parallel Sphere_ hath one _Pole_ of the _World_ in the _Zenith_, the other in the _Nadir_, and the _Equinoctial_ Line in the _Horizon_."

[209] PAGE 136, LINE 1. Page 136, line 1. _praesenti._--The editions of 1628 and 1633 read _sequenti_, to suit the altered position of the figure.

[210] PAGE 137, LINE 24. {52} 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's _Acts and Monuments_ with 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 entitled _Viridarium Moralis Philosophiae, per Fabulas Animalibus brutis attributas traditae, etc._ (Coloniae, 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 fable _Ferrarii fabri et canis_, representing the smith smiting iron on the anvil, whilst his lazy dog sleeps beneath the bellows. The cut on p. 139 of 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 words _Septrenio_ and _Auster_ have been added.

[Illustration]

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 original {53} plate, 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 words _Septentrio_ and _Auster_ are 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. 203 of 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 work _Le Diverse & Artificiose Machine_ of 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's _Viridarium_.

[212] PAGE 140, LINE 2.. Page 140, line 2. _praecedenti._--This is so spelled in all editions, though the sense requires _praecedente_.

[213] PAGE 141, LINE 21. Page 141, line 24. _quod in epistola quadam Italica 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, _Musaeum 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 ade 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 a 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, quae tractu temporis in magnetem conuersa est, & ab vno latere ferrum trahebat, & ab altero respuebat." See also Sir T.

Browne's _Pseudodoxia Epidemica_ (edition of 1650, p. 48), and Boyle's tract, _Experiments and Notes about the Mechanical Production of Magnetism_ (London, 1676, p. 12).

{54} Another case is mentioned in Dr. Martin Lister's _A 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 of _Chartres_. 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 Hire_ has Printed a Memoir of it; also Mons. _de Vallemont_ a 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's _Rudimentary Magnetism_ (London, 1872, p. 10).

"In the _Memoirs of the Academy of Sciences_ for 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 planetae & corpora coelestia._--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 the _nativities_ of 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 read _iisdem_.

[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 by _aciarium_ was meant edge-steel as used for blades. Barlowe, in his _Magneticall 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 the _Arte de Nauegar_ of Pedro de Medina (Valladolid, 1545, lib. vi., cap. 1).

[217] PAGE 149, LINE 8. Page 149, line 9. _per multa saecula._--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 stellae in cauda vrsae._--What Cardan said (_De Subtilitate_, _Edit. citat._, p. 187) was: "ortum stellae in cauda ursae minoris, quae quinque partibus orientalior est polo mundi, respicit."

[219] PAGE 153, LINE 21. Page 153, line 26. _sequitur quod versus terram magnam, siue continentem ... a vero polo inclinatio magnetica fiat._--Gilbert {55} goes 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.

In _Purchas 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 11-1/3 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 the _Philosophical 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 assertion _Variatio 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 our _Magneticall_ Philosophers) 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 former _Longitude_. For it is the Assertion of _Mr. 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 the _Sea-Mans Kalendar_ that in the year 1657 the variation would be zero at London. Compare Bond's _Longitude Found_ (Lond., 1676, p. 3).

As to inconstancy of the variation in one place see further Fournier's _Hydrographie_ (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 stand _perfecta_, as in line 10 below.

[221] PAGE 157, LINE 11. Page 157, line 13. _varietas_, for _variatio_.

[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 the _Mecometrie de l'Eyman_ of G. Nautonier (1602). Here the name _Borrolybicus_ is given as a synonym for _Nortouest Galerne_, or [Greek: Olumpias], while the two winds on the points next on the western and northern sides respectively are called _Upocorus_ and _Upocircius_.

{56} In Swan's _Specvlvm Mundi_ (Camb., 1643, p. 174) is this explanation: "Borrholybicus is the North-west wind."

In Kircher's _Magnes_ (Colon. Agripp., 1643, p. 434) is a table of the names of the thirty-two winds in six languages, where _Borrolybicus_ is given as the equivalent of _Maestro_ or _North-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. (See _Challenger Reports, Physics and Chemistry_, vol. ii., part vi., _Report on the Magnetical Results_ by Staff-Commander Creak, F.R.S.)

[224] PAGE 162, LINE 2. Page 162, line 3. _quare & respectiuum punctum ...

excogitauit._--The passage referred to is in _The newe Attractiue_ of Robert Norman (Lond., 1581), chap. vi.

"Your reason towards the earth carrieth some probabilitie, but I prove that there be no _Attractive_, or drawing propertie in neyther of these two partes, then is the _Attractive_ poynt lost, and falsly called the poynt _Attractive_, as shall be proved. But because there is a certayne point that the Needle alwayes respecteth or sheweth, being voide and without any _Attractive_ propertie: in my judgment this poynt ought rather to bee called the point Respective ... This Poynt _Respective_, is a certayne poynt, which the touched Needle doth alwayes _Respect_ or shew ..."

[225] PAGE 165, LINE 2. Page 165, line 2. _De pyxidis nauticae vsitatae compositione._--Gilbert's description of the usual construction of the mariner's compass should be compared with those given by Levinus Lemnius in _The Secret Miracles of Nature_ (London, 1658); by Lipenius in _Navigatio Salomonis Ophiritica_ (Witteb., 1660, p. 333); and with that given in Barlowe's _Navigators Supply_ (London, 1597). See also Robert Dudley's _Dell' Arcano del Mare_ (Firenze, 1646).

[226] PAGE 165 deals with the construction; the process of magnetizing by the loadstone had already been discussed in pp. 147 to 149. 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 the _Havenfinding Art_ (London, 1599), from which work the passage on p. 167 is 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 the Note to page 4. 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. "_Flavius_ saith, an Italian found it out first, whose name was _Amalphus_, born in our {57} Campania. 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's _Natural Magick_, English translation, London, 1658, p. 206.) See also Lipenius (_op. citat._ p. 390).

The pivotting of the needle is expressly described in the famous _Epistle_ on 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 (or _pyxis_) 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.