The first suggestion of suspending a magnetic needle by a thread appears to be in the _Speculum Lapidum_ of Camillus Leonardus (Venet., 1502, fig. k ij, lines 25-31): "N tacto ferro ex una [=p]te magnetis ex opposita eius [=p]te appropinquato fugat: ut ex[=p]i[~e]tia docet de acu appenso filo."

The earliest known examples of the "wind-rose" are those in certain parchment charts preserved in the Biblioteca Marciana in Venice. These go back to 1426 or 1436, the best being ascribed to Andrea Bianco. They have the North indicated by a fleur-de-lys, a trident, a simple triangle, or a letter T; while the East is distinguisht by a cross. The West is marked with a P. (see Fincati, _op. citat._). The eight marks in order, clock wise, run thus,

[Lily] (or T). G. [Cross] (or L) S. O. A (or L). P. M.

The letters correspond to the Italian names of the principal winds:

Tramontano North.

Greco North-East.

Levante East.

Sirocco South-East.

Ostro South.

Africo or Libeccio South-West.

Ponente West.

Maestro North-West.

Wind-roses marked with the names of the minor winds are found in Nautonier's _Mecometrie de l'Eyman_ (Vennes, 1602-1604, pp. 151-152), and Kircher's _Magnes Siue de Arte Magnetica_ (Colon. Agripp., 1643, p. 432).

The description above given of the early Venetian wind-roses _exactly_ describes the compass-card as depicted by Pedro de Medina in his _Arte de Nauegar_ (Valladolid, 1545, folio lxxx.), in the sixth book entitled "las aguias de navegar"; while in the _Breve compendio de la sphera_ of Martin Cortes (Sevilla, 1551, cap. iii., _de la piedrayman_) a similar wind-rose, without the letters, is found.

{58} In the _De Ventis et navigatione_ of Michaele Angelo Blondo (Venet., 1546, p. 15) is given a wind-rose, described as "Pixis uel Buxolus instrumentum et dux nauigantium," having twenty-six points inscribed with the names of the winds, there being six between north and east, and six between south and west, and only five in each of the other quadrants. In the middle is a smaller wind-rose exactly like the early Italian ones just mentioned.

In the _Della Guerra di Rhodi_ of Jacobo Fontano (Venet., 1545, pages 71-74) is a chapter _Dei Venti, e della Bvssola di nauicare di Giovanni Quintino_, giving a wind-rose, and a table of the names of the winds, the north being indicated by a pointer, at the cusp of which are seven stars, and the west by an image of the sun. The other cardinal points are marked with letters.

Barlowe, in _The Navigators Supply_ (Lond., 1597), speaks thus:

"The merueilous and diuine Instrument, called the _Sayling Compasse_ (being one of the greatest wonders that this World hath) is a Circle diuided commonly into 32. partes, tearmed by our Seamen Windes, _Rumbes_, or Points of Compasse."

It is a disputed point with whom the method of naming the winds originated.

Some ascribe it to Charlemagne. Michiel Coignet (_Instruction novvelle ...

touchant l'art de naviguer_, Anvers, 1581, p. 7) ascribes it to Andronicus Cyrrhestes. See Varro, _De Re Rustica_, iii., 5, 17, and Vitruvius, i., 6, 4.

Gilbert's complaint of the evil practice of setting the needles obliquely beneath the card, with the intention of allowing for the variation, is an echo of a similar complaint in Norman's _Newe Attractiue_. In chapter x. of this work Norman thus enumerates the different kinds of compasses:

"Of these common Sayling Compasses, I find heere (in _Europa_) five sundry sortes or sets. The first is of _Levant_, made in _Scicile_, _Genoua_, and _Venice_: And these are all (for the most parte) made Meridionally, with the Wyers directlye sette under the South, and North of the Compasse: And therefore, duely shewing the poynt _Respective_, in all places, as the bare Needle. And by this Compasse are the Plats made, for the most part of all the _Levants_ Seas.

"Secondly, there are made in _Danske_, in the Sound of _Denmarke_, and in _Flanders_, that have the Wyers set at 3 quarters of a point to the Eastwards of the North of the compasse, and also some at a whole point: and by these Compasses they make both the Plats and Rutters for the Sound.

"Thirdly, there hath beene made in this Countrey particulary, for Saint _Nicholas_ and _Ruscia_, Compasses set at 3 seconds of a point, and the first Plats of that Discoverie were made by this Compasse.

"Fourthly the Compasse made at _Sevill_, _Lisbone_, _Rochell_, _Bourdeaux_, _Roan_, and heere in _England_, are moste commonly set at halfe a point: And by this Compasse are the Plats of the East and West _Indies_ made for their Pylotes, and also for our Coastes neere hereby, as _France_, _Spayne_, _Portugall_, and _England_: and therefore best of these Nations to bee used, because it is the most common sorte that is generally used in these Coastes."

Bessard (_op. citat._, pages 22 and 48) gives cuts of compasses showing the needle displaced one rumbe to the East.

Gallucci, in his _Ratio fabricandi horaria mobilia et permanentia cum magnetica acu_ (Venet., 1596), describes the needle as inclined 10 degrees from the south toward the south-west.

The frontispiece of the work of Pedro Nunez, _Instrumenta Artis Navigandi_, Basil., 1592, depicts a compass with the lily set one point to the east.

Reibelt, _De Physicis et Pragmaticis Magnetis Mysteriis_ (Herbipolis, 1731), depicts the compass with the needle set about 12 degrees to the East of North. See also Fournier, _Hydrographie_ (Paris 1667); De Lanis, _Magisterium Natvrae et Artis_ (Brixiae, 1684); Milliet Deschales, _Cursus seu Mundus {59} Mathematicus_ (Lugd., 1674). Both the latter works give pictures of the compass-cards as used in South Europe, and in North Europe, and of the various known shapes of needles.

[227] PAGE 168, LINE 29. Page 168, line 33. _Directio igitur inualidior est prope polos._ Here as in many passages _direction_ means _the force which directs_. A similar usage prevails with the nouns _variation_ and _declination_, meaning frequently the force causing variation or declination respectively.

PAGE 172, LINE 13. _perquirere._ The edition of 1633 reads _perquirero_, in error.

[228] PAGE 172, LINE 29. Page 172, line 33. _Ad pyxidis nauticae verae & meridionalis formam ... fiat instrumentum._--An excellent form of portable meridian compass, provided with sights for taking astronomical observations, is described by Barlowe (_The Navigators Supply_, London, 1597), and is depicted in an etched engraving. An identical engraving is repeated in Dudley's _Arcano del Mare_ (Firenze, 1646). Gilbert's new instrument was considerably larger.

[229] PAGE 174, LINE 19. Page 174, line 21. _addendo vel detrahendo prostaphaeresin._--"Prosthaphaeresis, conflata dictione, ex additione et subtractione speciebus logistices, nomen habet ab officio, quia vt in semicirculo altero ad aequabilem motum adijcitur, ita in altero subtrahitur, vt adparens motus ex aequabili taxetur: atque hinc fit, qud quae Prosthaphaeresis dicitur Ptolemaeo, ea vulg aequatio vocetur." (Stadius, _Tabulae Bergenses_, Colon. Agripp., 1560, p. 37.)

[230] PAGE 174, LINE 28. Page 174, line 31. _Stellae Lucidae._--According to Dr. Marke Ridley (_Magneticall Animadversions_, London, 1617, p. 9), this chapter xii. of book iv., with the Table of Stars, was written by Edward Wright, the author of the Prefatory Epistle of _De Magnete_. Wright was Lecturer on Navigation to the East India Company, and author of sundry treatises on Navigation.

[231] PAGE 187, LINE 14. Page 187, line 16. _hic qui versus boream constitit ... meridionalis est, non borealis, quem ante nos omnes existimabant esse borealem._--Earlier on, on pages 15 and 125, Gilbert had mentioned this point. His insistence caused Barlowe (_Magneticall Aduertisements_, 1616, p. 4) to speak of the south-pointing end of the needle as the "true North," and thereby drew on himself the animadversions of Marke Ridley.

[232] PAGE 188, LINE 15. Page 188, line 16. _in recta sphaera._--See note to p. 134.

[233] PAGE 190, LINE 14. Page 190, line 19. _declinans in Borealibus._--Dipping as it does in northern regions; that is, with the north-seeking or true-south pole downward.

[234] PAGE 195, LINE 20. Page 195, line 24. _multa maiora pondera._--Many greater weights. All editions read _multa_, but the sense requires _multo_: "much greater weights."

[235] PAGE 196, LINE 10. Page 196, line 12. _constans est._--This must not be read "is constant," for it is constant only in any given latitude.

[236] PAGE 196, LINE 15. Page 196, line 18. _De proportione declinationis pro latitudinis ratione._--Gilbert here announces, and proceeds in the next seven pages to develop, the proposition that to each latitude there corresponds a constant dip to a particular number of degrees. If this were accurately so, then a traveller by merely measuring the dip would be able to ascertain, by calculation, by reference to tables, or by aid of some geometrical appliance, {60} the latitude of the place. In this hope Gilbert fought to perfect the dipping-needle; and he also worked out, on pages 199 and 200, an empirical theory, and a diagram. This theory was still further developed by him, and given to Thomas Blundevile (see the Note to p. 240).

Briggs of Gresham College, on Gilbert's suggestion, calculated a table of Dip and Latitude on this theory. It was found, however, that the observed facts deviated more or less widely from the theory. Kircher (_Magnes_, 1643, p. 368) gives a comparative table of the computed and observed values. Further discovery showed the method to be impracticable, and Gilbert's hope remained unfulfilled.

[237] PAGE 197, LINE 18. Page 197, line 21. _progressionis centri._--Note Gilbert's precision of phrase.

[238] PAGE 200, LINE 12. Page 200, line 11. _subintellig[=u]tur._--This is printed _subintelligitur_, and is altered in ink in all copies of the folio edition. The editions of 1628 and 1633 read _subintelliguntur_. Similarly in line 14 the word _ducit_ has had a small _r_ added in ink, making it read _ducitur_, as also the other editions.

[239] PAGE 203. This figure of the experiment with the simple dipping needle suspended in water in a goblet is due to Robert Norman. In his _Newe Attractiue_ (London, 1581, chap. vi.) he thus describes it:

"Then you shall take a deepe Glasse, Bowle, Cuppe, or other vessell, and fill it with fayre water, setting it in some place where it may rest quiet, and out of the winde. This done, cut the Corke circumspectly, by little and little, untill the wyre with the Corke be so fitted, that it may remain under the superficies of the water two or three inches, both ends of the wyer lying levell with the superficies of the water, without ascending or descending, like to the beame of a payre of ballance beeing equalie poysed at both ends.

"Then take out of the same the wyer without mooving the Corke, and touch it with the _Stone_, the one end with the South of the _Stone_, and the other end with the North, and then set it againe in the water, and you shall see it presentlie turne it selfe upon his owne Center, shewing the aforesay'd _Declining_ propertie, without descending to the bottome, as by reason it should, if there were any _Attraction_ downewards, the lower part of the water being neerer that point, then the superficies thereof."

[240] PAGE 212, LINE 7. Page 212, line 8. _ex altera parte._--The sense seems to require _et altera parte_, but all editions read _ex_.

[241] PAGE 213, LINE 1. Page 213, line 2. The passage here quoted from Dominicus Maria Ferrariensis, otherwise known as the astronomer Novara, does not occur in any known writing of that famous man. It is, however, quoted as being by Novara in at least three other writings of the same epoch. See the _Tabulae secvndorum mobilium coelestium_ of Maginus (Venet., 1585, p. 29, line 19 to p. 30, line 11); the _Eratosthenes Batavvs_ of Willebrord Snell (Lugd. Batav., 1617, pp. 40-42); and the _Almagesti novi (Pars Posterior)_ of Riccioli (Bonon., 1651, p. 348). The original document appears to have perisht. See a notice by M. Curtze in Boncompagni's _Bullettino di Bibliografia_, T. iv., April, 1871.

[242] PAGE 214, LINE 26. Page 214, line 31. _Philolaus Pythagoricus._

"Philolaus a le premier dit que la terre se meut en cercle; d'autres disent que c'est Nicetas de Syracuse."

"Les uns pretendent que le terre est immobile; mais Philolaus le pythagoricien dit qu'elle se meut circulairement autour du feu (central) et suivant un cercle oblique, comme le soleil et la lune."--(Chaignet, _Pythagore et la Philosophie pythagoricienne_, Paris, 1873.)

It appears that the first of these _dicta_ is taken from Diogenes Laert., viii. 85; and the second from Plutarch, _Placit. Philos._, III. 7. The latter {61} passage may be compared with Aristotle, _De Coelo_, II. 13, who, referring to the followers of Pythagoras, says: "They say that the middle is fire, that the earth is a star, and that it is moved circularly about this centre; and that by this movement it produces day and night."

[243] PAGE 214, LINE 34. Page 214, line 42. _Copernicus._--His work is _De revolutionibus orbium coelestium, libri vi._ (Basil., 1566).

[244] PAGE 215, LINE 27. Page 215, line 24. _quae ... in caelo varijs distantijs collocata sunt._--This remark appears to be Gilbert's one contribution to the science of Astronomy; the stars having previously been regarded as fixed in the eighth sphere all at the same distance from the central earth, around which it revolved.

[245] PAGE 220, LINE 6. Page 220, line 6. _quem nycthemeron vocamus._--The 1628 and 1633 editions read _nyctemoron_.