without many turnings to and fro so that neere the pole the direction is very strong neither by leuelling hindred Alwayes and in all places the Lilly of the compasse or crosse of the directory-needle standeth and is seated into the North both in this North side and on the other South side of the aequinoctiall line or circle of the earth Tab. III. Fig. 9. Tab. XII Fig. 13. contrary to the syte of the needle neere the Terrella or Semiterrella because they are touched and excited at that point of the Load stone that in his boate resteth South and being set at liberty from the Loadstone by the earth is turned North as the point touched at the North-pole of the Adamant is turned South neither needeth there here any conuersion of the compasses in sailing and going from one prouince of the aequator to the other as the needle idoth towards the Magnet being masculine and the needles of iron or steele feminine but the needles to the earth are perfect Magneticall bodies and do keepe their correspondency with the earth as if they were Magnet stones or diameters of little earthes therefore the needles and compasses passing from one side of the aequator to the other in a meridian and great circle proceedeth on still in a right line vniformely onely the points of the needles and compasses do take their turnes to be predominant in their direction in their owne prouinces especially if their leuel would suffer the vertue Inclinatory to preuaile which thing is most apparant by the Inclinatory-needle in his ring that being on this side of the aequator erecteth his lilly aboue the horizon towards the pole but on the further South side of the aequator dippeth his Lilly vnder the horizon and suffereth the Point to respect his owne pole with conuenient angles to the axis But this thing cannot be done by the compasse and directory-needle which lye alwaies paralel to the horizon but onely is demonstrable by the stone in the 4 and 5 tables before This were a fit place to speake of the order of making Sea-Compasses the instruments for Magneticall direction the making whereof is very well knowne vnto Artificers yet I could wish that they were more artificially made then they are though the price were some-what more with some additions which wee do partly touch in the Chapter following and wish also that the points were 48. in vse that euery point might be halfe an hower All direction is performed vpon the true Meridian respecting directly with the Needle the poles of the earth as the Needle doth in the good and pollished Load-stone and Terrella vnlesse it be weakened depraued and forced to decline from the true Meridian of the earth by the causes of variation CHAP. XXVI Of the variation of the Compasse from the true Meridian Tab XIII But because the Globe of the earth is knowne vnto vs to bee very vn-euen and vn-equally mixed with many materials differing from Magneticall substance hauing great and stony Mountaines large Vallies deepe Seas long and high Continents and fore-lands some with mighty scattered rockes of Loadstone of Iron-Mines and other Magneticall matter and some without as also the entrailes and interiour substance barke or scarfe of the earth consisting of a great quantity of substance not Magneticall whereupon it commeth to passe that when the Magneticall faculty of the earth shall direct these Magneticall instruments of the Needle and Compasse they are not composed or set directly vpon the true Meridian that passeth right on to the poles of the earth but are drawne and forced awry towards some vigorous and Magneticall eminency of the earth whereby the Meridian which the Needle and Compasse maketh doth decline and vary from the true Meridian of the earth certaine parts degrees in the Horizontal circle which is called the variation of the Compasse the Meridian that this declinatiō of the compasse needle maketh may be termed the Magneticall Meridian to distinguish it from the true Meridian and the space betweene the Magneticall Meridian and the true Meridian is the difference of variation So that here the needle Cōpasse do dispose themselues into the North and South obliquely and not truely and exactly and according to the diuersity and strength of the scattered Magneticall bodies being the causes of variation the arch of the declination is greater and lesser as in sayling by great Continents and High-lands Magneticall either the point or taile of the Needle and Compasse is forced awry towards the East or West as is demonstrated in the chapter of Applications in the XXIII Chapter For if the Magneticall eminency whether it bee iron like clay myne of iron or rockeof Load-stone be contiguous vnto the Magneticall Globe of the earth and fastened in the same substance vnto it then the Compasse and Needle will leaue the direction of the Magneticall Globe of the earth and deflect towardes this eminency but if this Mountaine Magneticall be not continued with the Globe and haue other Materials vnder and about him then the Needle and Compasse will be thrust awry and flye from it declining as much in a maner the other way leaning vnto it by the other point or taile as it is demonstrated in the rule of Application of one Needle in his varrying vpon the Load-stone vnto a peece of Iron touching and not touching the stone And no lesse doth the Needle and Compasse vpon the continent and inner-inner-land decline Easterly or Westerly when as a great part of the earth shall bee of a substance no way Magneticall and the other part shall bee of a vigorous and Adamantine quality to attract vnto it For although all direction to the North and South by the Needle and Compasse be from the vertue of the whole Magneticall Globe of the earth yet a strong effectuall and neere perticular cause though weaker as it is proued in the end of the XXIII Chapter varieth their direction diuersly and erratically by that Land especially which lyeth and treateth North and South Where as the vigor and potency Magneticall increaseth from the Equinoctiall to the poles of the Magneticall Globe of the earth as it doth in the Terrella whereby the like eminency Magneticall in the parts neere the poles be of more allicient and Adamantine property then they are about the Equinoctiall therefore it may bee thought that in sayling vpon one Meridian in like distance from this eminency enriched with this vigour it will make a greater variation of the Compasse neere the pole then it doth neere the Equinoctiall but this matter may bee helped and lessened by the great vigour that the needle is directed withall from the Adamantine Globe of the earth especially if the Seas bee shallow and the Needle in a neere Orbe vnto the same for thus the Needle will very hardly bee remoued because the force of the earth is great that directeth it but marke that in the XXIII chapter where a smaller strength Magneticall altereth quickely the
South or North may be termed by that part which it respecteth some haue laboured much to cleare If you chance to find out the rocke where the Loadstone doth grow where you purpose to take out a part of the same marke your part with notes for the North and South then cut out your peece out of the rocke and put it into a bole to swimme on the water and your markes will be turned to a contrary situation to that they had in the rocke and the North note will be turned South and the South North and so would the rocke of the great Magnet it selfe if it were so placed make the like alteration in his situation by the generall conformation and direction of the mighty Magnet the globe of the Earth Therefore the reason why that the Loadstone in the boat vpon the water turneth bendeth and seateth it selfe to a contrary situation to that he receiued and had primarily whilest he was in the bowels of the Earth and vnited with the body of the great Magnet is because that euery peece and part of a Load-stone being seperated from the whole whereof he was a part is now become a perfect complete and sole Magneticall body and is as it were a little earth of it selfe hauing all the proprieties Magneticall that the great Earth hath as his two poles meridians aequator and such like and therefore according vnto the nature of Magneticall vnion hereafter spoken of in the XXII chapter will in no wise indure and cannot be suffered to match and seate it selfe as he did before but thinketh it more naturall and a thing of more perfection and conueniency to turne his aspect a contrary way to that he had primarily at his first making and endowement with Magneticall vertue This alteration of polity is to be obserued likewise in Magneticall needles and long peeces of iron that be touched and animated and adhere to that part of the Load-stone which seateth it selfe North which being at liberty and seperated from the Loadstone will turne that part and end that was touched at the North pole and seate it alwayes in the South and it shall be sufficient for vse to know and marke with a note which is the North-pole of your Magnet and which is the South-pole There is another vertue in the Poles of the Loadstone and that is that the South-pole turned downeward will take vp more then the North-pole will and the North pole will erect a greater waight thâ—n the South part or pole will as some say Tab. III. Fig. 2. a b. But I haue alwayes obserued that the Pole of the Magnet that seateth it selfe North is alwayes the most vigorous and strong Pole to all intents and purposes vnlesse he lacke the quantity and like substance the South part hath These Poles which be in the great Magnet of the globe of the Earth haue a maruelous strong Magneticall power imparted vnto them that they cannot be turned either higher or lower or moued to the right hand or to the left but hold the Earth continually in a true and certaine position and place and would if any force or power should moue their great strength awry from the true syte and meridian latitude returne to their right syte and place againe and this is the true vertue of the Poles of globes which the Sunne and Iupiter haue as well as the Earth These Poles be most certaine and sure markes for all Magneticall bodies conueniently caried to direct themselues vnto Tab. III. Fig. 9. as appeareth by our Compasses which in all places of the world turne their Lilly into the North whereby the Marriner knoweth what course to take And the Magneticall Pole Poles of the world both articke antarticke are all one and not diuerse as some haue imagined which haue lost both their oyle and their paines and this is true by the demonstrations and motions of the Inclinatory-needle although there be many momentary causes of variation These Poles hold the Earth certainely in her polar position while she turneth her selfe about to receiue the Sun-beames and influences of the starres and planets for the generation and maintenance of all inferior bodies vpon her in her proceeding out of her Lastly these Poles of the Earth in certaine great number of yeares haue naturally a little inclination in the polar circles of the Zodiacke for the receiuing and moderation of the beames lights and influences of the starres whereby the progressions and anticipations of the aequinoctiall and the mutations of the greatest declination of the Sunne are perfectly vnderstood to preuent the faining of many Spheres aboue the starres as the ninth tenth and eleuenth and their impossible motions In fashioning the Loadstone it is conuenient to make flat or roundish the ends of the Magnet where the Poles are the better to cap and arme them with iron or steele to lift vp their conuenient waights Tab. III. Fig. 2. 12. and as the most are Tab. I. At the Pole the Inclinatory-needle doth not incline obliquely to the axis Tab. III. Fig. 6. as the needle c c to a b the axis as in other places but aspecteth the Pole directly and perpendicularly as Tab. III. Fig. 1. the needle c respecteth the axis b a directly maketh one line with it Also at the North-pole that point of the directory-needle and compas that did behold the South of himselfe being applied to the North-pole doth turne as some thinke but this is true only at the aequator in the spaces between the aequator the 34 degree as is demonstrated in the XII chap. not at the Pole it selfe and the places neere adioyning for at the North-pole if the Magnet be truely placed that point that pointeth towards the South doth point to the South directly and in the places neere adioyning doth it obliquely A wier touched Magnetically hath two Poles as Tab. III. Fig. 5. the one end a is North and b of the nature of the South CHAP. VII Of the Axis THe Axis or axeltree of the Magnet is a line that passeth from the one Pole to the other by the center of the body of the Loadstone and after this order there is an Axis vnderstood to be in the Earth Tab. III. Fig. 1. 2. 3. 9. 10. In fashioning of Magnets if a peece be taken away paralell from the Axis then in these two Loadstones the Axis with his poles will be remoued into the middest of the stone as Tab. III. Fig 3. a b the Axis in either peece is in the middest of the stone so whether that bunches be taken away from the Loadstone or any cauities filled the Axis will alwayes be placed in the middest of the most vigorous bulke of the Load-stone as a b in euery figure It is said in the latter end of the V. chapter that if a Loadstone be sawen in two parts from one pole to the other vpon the Axis that the poles and Axis will be found in the
middest of the bulkes of the two peeces paralell to the old Axis Tab. III. Fig. 3. and the poles of the lesser peece will be altered Also when as a side of the Load-stone shall be made flat and paralell to his Axis that side will attract hold and vnite vnto him long peeces of iron sidelings and paralelly Tab. III. as Fig. 4. c the peece of iron is adioyned paralelly to a b the Axis as the pole erecteth perpendicularly to it Tab. III. Fig. ◠the waight c is attracted plim-wise to the Axis a b. And also two Magnets somewhat long in forme swimming in their vessels vpon the water wil adhere and vnite in a meridian paralell to their Axis Tab. XI Fig. 5. that if one of their vessels be haled the other vessell with the other Magnet his loading will follow both being fast grapled together so that they cannot part asunder Likewise take two Magnets that be armed with their teeth of iron or steele descending from these poles at right angles to the Axis to take vp with both teeth together haue their Axis both of one length as Tab. III. Fig. 12. place the teeth descending from the South-pole vnto the teeth that haue the vigor frō the North-pole and they will cleaue and vnite together as one body and Load-stone paralell-wise to the Axis and the one though he be the weaker will lift vp the heuier perpendicularly Also all Magneticall bodies whether it be at the aequator at the poles or at any intermediall part betweene these two do all of them apply conforme and vnite their bodies together according to a correspondency of their Axis as shall be declared hereafter and not with their center to the center of the others body If a wier be touched Magnetically at one end the vigor will run through all the wier or Axis and haue a contrary vertue in the other end the one North the other South and halfe the Axis will be of one nature and halfe on another Tab. III. Fig. 5. the end of the wier at a is of the nature of the North-pole and the end at b is of the South-pole We sayd in the IIII. chapter that the Moone doth alwayes turne one Pole of her body toward the center of the Earth and moueth neerer further from the same as if that a long axeltree were passed through her body fastned in a ioynt to the center of the earth on which she should make her Epigeum and Peregeum in like maner it is to be probably gathered that the earth may naturally haue a Helicall Spirall vertue to moue on the Cilinder of her Axis in spirall lines not vnlike the arches of the longitude of the day to performe the Zodiacall motion partly illustrated in the XXII chapter by the bead in an instrument of rings for the finding of the variation where the bead as an earth is placed in the Axis higher and lower according to Zodiacall direction and Magneticall vertue will permit this spirall motion like as the sap passeth in the earth from the North hemisphere to the South prouince It is a thing worthy of better obseruation from the Truncke-glasse to know whether the Axis of Iupiter and the Sunne be paralell one to the other and with the Axis of the Earth which is to be examined by the turning of the spots about CHAP. VIII Of the Aequator IN all Magnetical bodies there is an Aequator or middle fence that diuideth the whole body in the middest betweene the two Poles like a middrift into two equall parts hemispheres and prouinces outwardly in the middle part in the greatest circumference from the poles there is an Aequator circle or line that deuideth the North-part of the stone from the South part as by a border-marke so that if a directory-needle touched Magnetically be conueyed to any part betweene this Aequator and the poles presently the end of the needle that is of the nature of the other prouince beyond the line of the Aequator will turne about from that part and the other end of the needle that hath affinity and naturall conformitie with the pole of that prouince will offer it selfe as Tab. III. Fig. 6. 7. 9. 10. in the prouince of the North-pole a aboue the Aequator and pricked line the bearded ende of the needle doth only offer it selfe and desire to apply and vnite to that part but the crosse end of the needle wil flye from it so this crosse end of the needle will only affect to behold the south prouince vnder the Aequators pricked line to the pole b and the bearded end of the needle will shift away This assertion is not only found to be true in the Loadstone but also in other formes of iron and steele and in the great Earth it selfe As take a round plate of iron that hath laine some time quietly without stirring as Tab. III. Fig. 6. or a ring of iron Tab. III. Fig. 7. and offer the sides of this plate or ring vnto the needle turning them about and the bearded point of the needle will respect the one halfe of these iron circles and the crosse part of the needle being of the nature of the other semicircle will apply and haue respect thereto Here in these iron formes the Aequator and limit of the two semicircles is better perceiued where it should be marked then the poles are for when the Magneticall needle is once past the bounds of the Aequator presently he turneth about his other point that respecteth the contrary semicircle or rather hemisphere the which for distinction sake might be painted of a red colour Moreouer if a directory-needle or Marriners compas be placed neere the Aequator of a Loadstone of these iron formes or of the earth they will situate themselues paralel to the axis of the poles as Tab. III. Fig. 6. 7. and Tab. VI. Fig. 1. Tab. VII Fig. 1. 2. and incline neither to one pole or the other being placed in a right sphere where the poles lie in the Horizon the needles standing in equall ballance with the Horizon looking North and South paralell to the axis Whereas it hath bene declared in the VI. Chapters before of the vigor of the poles that the vigor and strength Magneticall proceedeth by little and little from the Aequator to the poles increasing in their passage by the meridians vnto the poles to the end to augment their vertue of retaining consisting most firmely and constantly in the North and South wherby the Aequator of the earth is left voide of all vertue of consistence and left free or rather depriued of constancy and retaining of any firme situation and remaining naturally by reason of his great circumference and weake renitency most apt and prone for circular motion which by her star like vigor and intelligence hauing this her globous body so firmely fastned naturally in her poles as it were in two strong pillars and fitted in the Aequator and paralels as
in Chariot-wheeles for circumuolution turneth her selfe daily about from the West into the East to meet with and receiue the pleasant beames and influences of the Sunne Starres and Planets for to cherish comfort and inuigor all those goodly creatures that be placed vpon her grow out of her or be bred and conceiued in her as also for the continuall change and vicissitude of seasons being a thing more naturall and fit that the earth should thus moue for her owne good then that all the heauens should furiously moue to serue her It is to be obserued in fashioning of the Magnet stone that when the axis of the same shall be cut shorter that then the Aequator remoueth necessarily to the middest of the body of the Loadstone as if a long Magnet should be sawne and deuided into two peeces as Tab III. Fig. 8. vpon or paralell to the Aequator the poles will be in the middest of the stones and the Aequator will also be in the middest of either stone as a b and the pricked lines be For euery peece and part of a Loadstone hath his poles and Aequator with the rest of the circles as well and as naturally as the earth or any great Magnet hath and will be deuided into two iurisdictions by his Aequator though before all his part was but of one prouince and nature Euen so if you part a needle or long wier Magnetically touched in two peeces the parts will haue their seuerall poles as Tab. III. Fig. 5. the poles a b are in either part of the wier CHAP. IX Of the Meridians THe Meridians be great circles drawne by the aequator vpon the Loadstone or as may be obserued by the needle vpon the face of the Earth from the one pole to the other where they do all touch as in the centers Tab. III. Fig. 9. they be naturally in euery Loadstone and in the earth and are thus found out for they be the pathes whereon all Magneticall motions are trauersed and directed Lay a wier of a reasonable length vpon the Magnet as Fig. 9. a b and it will turne and seate it selfe vpon a Meridian and point to the poles and if he be moued from the Meridian by any force he will soone returne to the same againe and by this wier you may marke out a Meridian Likewise take a little directory-needle of a small diall and set it vpon a small pinne with a foote setting them vpon the Terrella Semiterrella or any Magnet Tab. III. Fig. 9. and the needle will point towards the pole make a marke remouing the needle forward and make more then ioyne all the points together which make a part of a Meridian and being continued forward runne to the pole so a small and short wier placed vpon the Magnet from place to place betweene the aequator and the pole will sticke fast at one end and erect the other obliquely and the seuerall places being noted with chalke or emery will set out a Meridian to the pole at the aequator being no longer then a barley corne will lie flat to the stone put him forwards toward the pole and then he will erect himselfe a little sticking at the other end vpon your Terrella Semiterrella or Magnet put him more forward and he will be erected lesse acutely and about 34 degrees from the aequator he will make a right angle with the axis of the Magnet and being brought and placed vpon the pole standeth vpright in one continued axis with the axis of the Loadstone Tab. III. Fig. 9. This variety of application to the Magnet doth produce a certaine kind of motion Magneticall which may be called the motion of inclination conuersion or conformity of one Magneticall body vnto another but the little directory-needle demonstrateth this motion best being caried about the Terrella and Semiterrella as shall be demonstrated in the XII Chapter following I haue spoken before somewhat as concerning the making flat of a side of the Loadstone paralell to the axis which is a Meridian line paralell thereto whereby waight may be apprehended Tab. III. Fig. 4. Therefore hauing a Magnet stone first made flat at the ends where the poles are and after a side made plaine and straight paralell to the axis for a Meridian then you may forme the stone into what fashion you please as into a foure-square into a figure of 5 6 or 8 equall angles or sides or into vnequall sides as hath bene thewed in the first Table in many types Cut a part from a Magnet stone meridionally and that end which was placed South when it was whole being seuered will turne North though naturally at first it was the South point as in Tab. III. Fig. 3. the poles a b in the little peece are turned contrary to the poles a b in the greater Magnet CHAP. X. Of the Paralels THe Paralels be circles and parts equidistant from the pole and Paralell to the aequator and do possesse the whole space betweene the aequator and the pole as Tab. III. Fig. 10. these circles are pricked out as the aequator is and are found by the Inclinatory-needle being caried at one angle about the Terrella and in all these places the small wiers Tab. III. Fig. 9. and directory-needles Tab. III. Fig. 10 do apply their axis or line of length obliquely to the axis of the body of the Magnet a b or of the earth For to find out these oblique angles in euery Paralel and what correspondency they haue vnto them there be diuerse operations diagrammes instruments and calculations found out to demonstrate and to know what angle of inclination will answer to euery Paralell for in euery Paralell of the earth the Inclinatory-needle maketh a diuerse angle of inclination to the axis but one angle and of one sort in one and the same eleuation of the pole or Paralell and by this meanes of the Inclinatory-needle in a ring the latitude of the pole is knowne on both sides of the aequinoctiall without any sight of the Sunne and starres by the Magneticall disposition from the earth If in forming of the Loadstone some Paralels be cut away as it should seeme in the Terrella by cutting and flatting the end where the pole is Tab. III. Fig. 11. yet in truth they remaine still vpon the Magnet though the Meridian lines be changed from crooked lines to straight lines and this is to be obserued that alwayes the Paralell neere 34 degrees in the perfect Terrella Semiterrella and round Meridian or straight Meridian where the directory-needle aspecteth that edge or angle at right angles vnto the axis Tab. III. Fig. 11. and Tab. VII Fig. 2. as the most protuberant and middle place betweene the pole and the aequator as in this Load-stone truncated and flatted at the pole In the Paralels of like distance from the pole all Magneticall bodies do apply and conforme alike and haue the like inclinations of their axis that denotate like eleuations of the
make right angles with these two poles of one nature as Tab. VIII Fig. 1. Now take away one of these stones and after turne the North-pole A towards the needles that behold the South-pole B of the other stone and they will all of them situate themselues equidistant-wise and at right angles to the aequators of both stones as Table VIII Fig. 2. Tab VIII Moreouer take other two Magnets that are long with the poles in the ends like that Tab. VII Fig. 2. and lay it before you and place three needles before it two at the end one in the midst against the aequator which will apply paralell to the axis of the stone and those two at the ends will seate themselues at right angles to the axis as before then set the other long Magnet that hath his poles in the ends with the North pole A against the North-pole A of the first stone Tab. VIII Fig. 3. and all the three needles will apply themselues in a straight line paralell to the axis somewhat like the order of the first type yet contrariwise Now take away this second stone with the poles in the ends turne it and place the South end B against the North end A as Tab. VIII Fig. 4. and then the 3 needles will stand at right angles to the axis and paralell one vnto another and to the aequator This is to be obserued in these applications that the neerer the second Loadstone is placed to the needles in aspect with the first Magnet the better will they shape out these figures of applications in the approching they will vary by little and little from their first situation vntill the vertue of the two Loadstones be equall in their orbe It may be imagined that these applications for the most part should be found naturally vpon the earth in trauelling or nauigating betweene two great Ilands or high Magneticall continents but the first fourth figure of this eighth Table cannot be found naturally in any place Tab. VIII Fig. 1. and Fig. 4. There is also much variety of variation in one needle neere two Magnets or a Magnet and Magneticall body as place a needle on a little foote vpon the Terrella Semiterrella or Loadstone and it will direct it selfe rightly vpon the meridian of the stone as hath bene proued before Tab. III. Fig. 9. but if you hold a little peece of iron toward the point of the needle the point will flie from the iron and deflect from his meridian a little Yet let this peece of iron touch the Load-stone and be vnited vnto it and put it towards the needle a farre off and the needle will turne from his meridian and decline and vary towards it the contrary is to be sayd if this iron be put towards the taile of the needle Now take two long Magnets that haue their poles in the end and place a needle before the aequator of one of them and it will apply paralell to the axis then bring the other Loadstone and place the end where the pole is against the aequator of the first Loadstone as Ta. VIII Fig. 5. and then the needle will vary his position and seate it selfe at right angles to the axis of both Magnets So also take two Loadstones and let one of them haue the poles in the middest and the other in the ends and you shall behold much artificiall variety of the application of one needle vnto them Place a needle before the middest of the Loadstone that hath his poles in the middest and it will behold the pole after lay downe the other Magnet that hath his poles in the ends and set his aequator against the needle and it will vary his position and stand paralell to the aequator of the former Magnet whose pole he beheld before as Table VIII Fig. 6. Tab. IX Set a needle against the end of the Load-stone that hath his poles in the ends and it will rest it selfe at right angles to the axis then apply the second Magnet to the needle that hath his poles in the middest Tab. IX Fig. 2. and the situation of the needle will be altered to be paralell to the axis he beheld at right angles at first Place at the corner of that stone that hath the pole B in the middest a needle and it will apply obliquely then lay the end of the other Loadstone that hath the pole A in the end and the needle will apply at right angles to the axis of both the stones as it is Table IX Figure 3. But set a needle afore the end of the stone that hath his pole B in the middest and set the end of the other Magnet that hath in the end the pole B of the same denomination as Tab. X. Fi. 1. and the needle will apply as is to be seene in the type in a straight line to the last and paralell to the axis of the first Also apply the aequator of this second stone that hath the poles in the endes vnto the needle placed as afore vnto the first stone Table X. Figure 2. and the needle will be paralell to both axis let the needle stand against the corner of the first stone obliquely and apply the end of the second stone with the pole in it Tab. X. Fig. 3. and the needle will apply as in the Tab. IX Fig. 3. Tab X CHAP. XVI Of preseruing the vertue of Magnets HAuing treated of the parts of the Magneticall bodies of their motions and applications now we will speake of his other naturall vertues and properties Some haue thought it very conuenient to keepe the Loadstones in filings of steele and iron to preserue their vertue and vigor thinking that the Magnet is fed or at least very much refreshed with them because they will cleaue so fast to the sides neere the pole But I do not allow this way so good to preserue them rather I like the keeping of them in a bag or cloute of woollin-cloth close from the iniury of the heate and cold of the weather or in a case or boxe fit for them and it is very necessary to wipe them often from dust and grease and to haue a care that they do not rust Also it is very commodious and naturall for them that they be layde vp and placed according to that naturall situation the which they would affect and respect if they were caried in a place and fashion free from renitency and resistance in the aire or water therefore they would be laide vp or hung accordingly as their poles and pointes do particularly respect to the North and South which will comfort them exceedingly Besides if the Loadstone be sometimes polished it will strengthen and releeue the body of the Magnet very much If a weake Magnet be rubbed at one of his poles with a stronger Loadstone he will be bettered by it in his vigor and vertue if not augmented therein Set a Magnet of no force or strength
that can easily be perceiued vpon a Loadstone of good strength and vigor especially vpon his poles and he will shew a vigor as if he were as strong as the Loadstone is whereunto he is vnited but after that he is taken away he will be as weake as before vnlesse it be often done CHAP. XVII Of contributing the vertue Magneticall to Iron or Steele THe iron barres in windowes being there placed North and South do receiue a polar vertue and directory faculty in time from the vigour of the orbe of the Magneticall globe of the earth and hauing marked them with notes to know which end was South which North in the window take them out and tye a thrid about the middest of them that they may hang leuelly in the aire and the end with the South note will turne it selfe into the North and the other note will behold the South contrary to their place in the window where they were first animated Magnetically Likewise if a long peece of iron be forged North and South and laide by to coole in the same situation he will be animated and indewed with a polar vertue and moue in the aire being hung in a thrid or put in a boate on the water and turne to the contrary pole to that from which he first receiued the Magneticall vigour If a rod of iron a wier or directory-needle be ouer-heat in the fire so that they haue lost all Magneticall vigor to direct them North or South yet let them be touched with the Loadstone at one end only and they will be excited with a directory and polar vigour at both ends and the one end of the semidiamiter will be of the North and the other of the South prouince and nature and being placed according to Magneticall orders will direct their points to the North South contrary to the pole that animated them with this vertue polar Also take rods of iron wiers and Magneticall needles that haue neuer bin touched with the Load-stone and rub them vpon the poles caps or teeth of the Loadstone at the ends and they will be much refreshed vigorated and animated with the polar and directory vertue at both ends both of the North and South-poles as though they had a new life of quicknesse infused into them and these shall refresh other needles that shall be touched with them and apprehend and draw them away like captiues and will not let them loose from them vnlesse by force you seuer them The best way to touch incite and giue the polar directory and Magneticall vigour and faculty vnto needles Marriners compasses is to rub them from the middest of the needle where the aequator of their axis is vnto their points vpon the pole cap or tooth of the Loadstone drawing them thus from their middle to the ends vpon the cap pole or paralell neere the same vnto the axis or at right angles to it thē after draw the other end vpon the other pole cap or tooth diuerse times as afore and these needles wiers and plates for compasses shall be perfectly touched and vigorated In long Loadstones that haue the poles in the ends if a wier be drawne paralell to the axis from the poles end to the aequator it will be incited with that pole It is doubted whether the touch and polar vertue wil be giuen as wel from a paralell some distance from the pole as from the pole it selfe it is plaine that from those paralels and parts neere adioyning to the pole the greatest vigour of politie Magneticall doth proceed yet in paralels neerer the aequator it will be giuē likewise the vertue directory will be very sufficient If you touch the needle amongst the paralels it is the best way to rub the needles alongst the meridians towards the pole rather then to rub the crosse the meridians in a paralell manner yet this way will giue the polar and Magneticall vertue also Some haue thought it better to touch compasses and Magneticall needles rather on the Loadstone then vpon their caps thinking that the vigor and faculty Magneticall will continue longest that is giuen from the bare Magnet stone the truth is to be obserued in time Yet the cap and tooth giueth and imparteth a stronger vigour to the needles then the bare stone doth because the vertue of the Loadstone is increased as much by the armor and cap as if his bulke simply were tripled Needles and wiers of steele heated to an height and reduced backe to a blewish colour will receiue a stronger touch and retaine it ten times longer then iron will howsoeuer he be hardned yet iron is best for caps placed neere the stone That end of the needle whether directory or inclinatory which is to be touched ought to be somewhat lighter then the other especially for the North and most vigorous touch end of the stone because that the touching will sway downe a little and the needle hath two motions one of direction the other of inclination and then the needles and compasses will play more leuell and aequidistant to the horizon for the sayd vses When any Magneticall needle or wier is touched from the North-pole or tooth of the Adamant that end of the needle will respect the North-pole of the Magnet but being seuered out of the orbe of the Adamant it will be directed into the South by the Magneticall vertue of the earth But if a round globe or ring of iron be touched with the North-pole of the stone the place touched will haue the vertue of the South-pole the North-pole will be in the opposit part and being seuered from the Magnet it will not turne to the contrary part as it falleth out in long Magneticall needles compasses as before If a ring of iron be touched the correspondent pole will be in the opposite part but if this ring be cut asunder and made a straight wier then both ends will haue the vigor of one pole onely Excite a directory needle at both ends from one pole and they will both be of one nature and looke what point was last touched and that will turne as if he onely were touched and direct more surely with lesse wauering too and fro then the other touchings will spoken of before Let a long peece of clay newly burnt coole North and South and it will receiue power Magneticall from the earth Set two Loadstones with their poles of one denomination at the ends of a peece of clay whilest it cooleth and both ends will be of one nature If a long wier be touched in the middest by the Loadstone and passed through a corke and set for to swim in the water it will wauer vp and downe vncertainely as though it were not touched but if it chance to rest it selfe towards the pole in time it will be indewed with his vertue Set a peece of iron vpon a Loadstone as you did a weake Magnet in the end of the former chapter and
he will leese all his potency polare and directiue faculty It is also conueient to vnderstand that hauing touched and animated a Needle Magnetically if contrary to this excited the Needle be rubbed from the point to the middest vpon the pole of a Magnet cap or tooth so any long peece of Iron or Steele else as knife dagger or sword which before would haue attracted and lifted vp Magnetically other Irons of some weight by being thus rubbed backe againe from the point to the middest haue that vertue taken away which they receiued before from the Load-stone and are as void of all vertue attractiue as they were before they touched the Magnet so that they neither will adhere or lift vp the least weight which was nothing to that they would haue done being excited If two Magneticall bodies be ioyned together at their poles these two poles that touch together haue the nature of the aequator and will not then excite or hold a needle thus touching An Adamant doth loose much of his strength if hee bee diminished and haue any part of his body taken from him especially if his figure was good before Some haue thought that certaine formes of the Magnet which may be allowed for conuenient figures do lessen the Magneticall vigour chiefly in their attraction as a sphericall or plaine superficies in the poles of globes and of square and angulous figures but these full and obtuse superficies and flat formes at the poles do attract best with their cappes and lift vp most as hath bene declared in the eighteene chapter before for this vigour proceedeth from the substance of the Adamant better then in long and piked formes which haue very little substance left about the poles yet this assertion is partly true in such like formes of Iron for in this mettle the long fashion is best A round plate of Iron to the pole cap or tooth of the Magnet disperseth and diminisheth the direct extent of his vigour like-wise a long plate or square peece of Iron or Steele Tab. II. Fig. 9. 17. applied to the two teeth of the Load-stone doth deforme the figure of the body and depraue his vertue CHAP. XX. Of the Commutation of the vertue Polar THe Polar vertue is said to be changed when as the North-pole is made the South-pole and the South-pole altered into the nature of the North-pole in Magneticall bodies this thing is effected in a weake Magnet by placing him a long time by a Magnet that is stronger vnnaturally which is done by adioyning the two North-poles or the two South-poles of the two Load-stones together a long time where the strong Magnet will by his neighbour-hood take away that contrary nature of pollity that was in the weake Load-stone and will make and infuse into him that polar vertue which doth naturally vnite vnto the pole of the strong Adamant making that point and pole to be South which was North. This thing is not onely experienced in two seuerall Magnets lodging together in one chamber and boxe but also if you shall agglutinate and cement diuers Magnets of diuers strengths together they will all of them be conioyned and vnited together as if it were one stone and body and may bee made and fashioned into a conuenient figure and will be endued with one vigour Magneticall of one prouince though separated they were of diuers polities and iurisdictions Magneticall needles and long formes of iron as kniues daggers wiers and such like if at one time they be touched and excited with the North-pole and made of his nature in all operations Magneticall then another time let these North points be touched as is vsed to be done with the South-pole of the Loadstone this end now hath lost his former nature and is made of affinitie and allegeance vnto the South-pole and after if you shall bestow vpon him by touching him againe at the other pole the vertue of the North-pole againe and then he will march vnder his banner and looke by which pole he is last touched and relieued he will remaine at his seruice alwayes after and beare his badge Put clay of a long forme in the fire after let him coole North and South and it will receiue a polar vertue after burne it againe in the fire and let that end which cooled first North now coole South and it will be commutated into the nature of the South and the other North. Furthermore if a strong Loadstone be held somewhat neere such compasses and needles as haue bene excited and touched with the vertue directory from the north by the Magnet although they be in their boxes yet the other end of the Loadstone will alter their situation and the Lilly of the Compasses will be cleane turned that that part and Lilly that should alwaies turne North will either stand South or else moue vp and downe vnperfectly and weakly hauing his first polar vertue changed for another or else taken away This conclusion maketh many affraide to let two Magnets come too neere together lest the one should rob the other but this will not be effected presently in the Loadstones themselues though that it be proued soone to come to passe in the Magneticall bodies of steele and iron If a directory-needle be excited at both ends from one pole it will haue the vertue of that pole at both ends but if both ends be rubbed backe from the points to the middest on the same pole both ends will haue the nature of the contrary pole and if one end be passed from the point to the middest that end will haue the nature of the contrary pole and the other end will keepe his nature still CHAP. XXI Of the discord of the two Points of the Adamant THis Proposition is demonstrated by two Magnets swimming in their boates in a bason of water as Tab. XI Fig. 5. 6. for if by force their two North-poles or South-poles be placed together they will abhorre the one the other and part asunder by speedy flight Tab XI When two Adamants shall confort and keepe together at their contrary poles at the approching of a third Magnet they will be separated and flie asunder Tab. XI Fig. 1. because that the pole of their Adamant that is offered vnto them is of the nature of the pole of one of the two Loadstones which the stone of that denomination perceiuing flyeth away from the company of the other because two South-poles and two North-poles in diuers Magnets be at discord and war together and cannot abide to dwell as neighbours together but each of them placed out of the others Orbe will both aspect the North with their North-poles and the South with their South-poles and thus two needles excited as Tab. XI Fig. 2. will each of them out of the others Orbe haue respect to their propper pole but if the needles bee within the Orbe one of the other as Tab. XI Fig. 7. then they will moue and adhere together at their contrary poles
retention of the whole more vigorous Magnet Also it is thought that the variation of the compasse is much furthered by the naturall inclination of the needle and his conformity to an high-land along the Meridian betweene the aequator and the pole like the demonstration of the Tab. VII Fig. 2. where the long Load-stone varieth the Needle from the Meridian by little and little to a right angle so if it could bee found out that a neere perticular cause were so potent to vary the needle as the long-stone there is the side of the land would vary much but the cap farre more also at the aequator as in the Tab. VIII Fi. 5. an eminent part of land ending at the aequator might vary the needle much as is there demonstrated Although these applications be great inducements that there should be such positions of the Compasse in some places betweene vigorous lands to be obserued yet because that these eminences from land are not any particular and complete Magnets of themselues but adherences and protuberances of some part of the Magneticall Globe and haue their nature according to the vigour of that paralell where they stand and haue not euery one of them a pole neere their caps and angles as these Magnets haue in their demonstrations set downe I cannot wholy approue them for sufficient demonstrations of variation though they may helpe very much for the vnderstanding of the same Therefore for the better knowledge of the variation of the Compasse by the Terrella it is very conuenient to apply a strong Magneticall body vpon the Terrella alongst the Meridian or a little obliquely then carrying a little needle vpon the Terrella the needle will vary more from the true meridian neere the aequator then it will doe neere the pole because the Needle neere the pole is directed very strongly and stiffely by those parts and will hardly bee forced from his direction But let the eminency bee very vigorous thicke and about twenty degrees high then hold the Needle so high from the Terrella in that Orbe then the Needle is to be conueyed from the aequator to the pole and first bring this eminence towards the Needle and it will beginne to vary from his direction being within twenty degrees or parts of the eminency and so increase his declination continually till hee bee varied towards sixty degrees in the parts neere the aequator and about fifty degrees at the most in the parts neerer the pole in the same Orbe therefore the deeper that the Seas are the greater is the Magneticall Orbe and the more subiect to suffer the Needle to bee attracted by a neere eminency and the shallower that the Sea is the lesse is the Magneticall orbe of the earth which more hardly suffereth the Compasse to vary This is to bee noted that high-eminences and lands neere the poles being before the Compasse doe not cause the same to decline but onely such eminences as are placed according to the Meridians and trent North and South or obliquely a little on either side to these the Compasse will be attracted awry from his true direction But if there be a narrow passage betweene two high-lands then the Compasse and Needle will respect neither eminency but carry and direct it selfe paralelly betweene them both when the strength of two high-lands is of equall force as it is demonstrated vpon the Terrella and not vnlike to the figure Tab. VIII Fig. 3. This is to be obserued also that the middest of an high-high-land by demonstration vpon the Terrella doth attract most and make the greatest variation and towards the ends it decreaseth by little and little and once passing by the eminency it varieth the compasse no more and it is likely so to do vpon the earth If there be a Magneticall rocke lying sidelings vnder the water it will make the needle vary a little from the true Meridian Therefore the farther that the Compasse is distant from an high-land that attracteth the lesse is the variation and passing further out of the orbe of his vertue there will be no variation at all vnlesse the deepes and substance of the earth bee partly Magneticall and partly of different substance For these causes it is obserued that places of a small distance assunder do differ much in their variation holding one proportion neither in passing vpon a meridian or on a paralell yet in one and the selfe-same place variations neuer differ but remaine certaine and constant The West-shore of a magneticall continent doth make the variation of the compasse Easterly and the East-shore of a maine-land beholding the Sunne rising attracteth on the North-side of the aequator the Lilly of the Compasse that it decline West from the true Meridian on the South-side of the Equinoctiall the point of the Needle is attracted Table XIII Fig. 1. 2. About the Ilands of Azores the Compasse hath little variation as at Fayall the Compasse varieth to the East three degres and at Coruo the variation of the Compasse foure degrees to the West Some thinke that Ilands though Magneticall make no variation being too weake and feeble in regard of the great strength of the directiue globe of the earth which directeth the needle and compasse because that the Iland of Elba neere Florence being ful of Loadstones causeth no variation of the compasse more then other places neere adioyning do but if vpon the Terrella as in the XXIII chapter there be neuer so litle wiers applied neere a needle it will deflect towards them so that here perfect obseruation may be desired which by the common rules is long and tedious to performe therefore I will set downe ready and easie wayes to obserue the true meridian by the Sunne that the variation of the compasse may be plainely perceiued and that in a moment by one obseruation only to the end that industrious and skilfull pilots will in time furnish themselues and the world with the true obseruation of variations in all parts of the world CHAP. XXVII Of finding the variation of the Compasse by one obseruation FOr this purpose there are certaine things to be knowne and obseruations to be had in a readinesse before this conclusion be found out first the place is to be set downe by name or note where this obseruation is made then the altitude of the pole in that place is to be knowne and set downe after the day of the moneth and the declination of the Sunne are to be set downe all these things skilfull pylots know very well to performe Then hauing a good sea-compasse for the water and a large directory-needle for the land it is necessary vpon the outmost part and circle of these to haue a limbe or verge a quarter of an inch broad for the horizontall circle and to haue the one halfe of it deuided into two ninties of degrees with his conuenient parts and figures as is vsuall in all quadrants beginning the numbers from the meridian-line and ending them at East and