wiar and fit the needle so that it hang precisely euen vpon this wiar insteed of an Axletree then touch him with the Loadstone and you shall presently see the end that should point towards the North decline or bend downe to his due place of declination if he be placed in the Magneticall Meridian set a little peece of waxe or any other thing vpon the contrary part for a counterpoyse that the needle may stand paralell with the Horizon then if it stand at right angles with that verginall wiar it is certainly in the Magneticall Meridian otherwise it will neuer stand at right angles but will make his sharper angle alwayes towards the Magneticall Meridian So that hanging in this counterpoise if you turne about the wiar vntill the needle doe make right Angles with it then doth the needle by his directiue vertue poynt vnto the Magneticall Meridian line Take off the counterpoise then it sheweth the declination for that place and by consequent the Latitude if you in that manner place him in the Instrument of declination so that one and the selfe same needle in the same place onely by taking off and putting on a little peece of wax sheweth plainely both those properties of directions and declinations as in like manner euery inclinatory needle will doe if the poynts of his Axis be sharpe and held in his boxe paralell vnto the Horizon he will shew both those properties of direction and declination A fine peece of corcke or leather or any tough snbstance may serue this needle for a counterpoyse in all Latitudes by thrusting it towards the center in lesse Latitudes and towards the end in the greater and I thinke it not impossible but that a skilfull Geometrician may so graduate the one halfe of such a needle that it alone with his counterpoyse may bee a meanes to giue a probable coniecture for the Latitude of any place whatsoeuer CHAP. VIII A discouery of errours committed in making and touching Magneticall Needles and Wyars of sayling Compasses with an aduise for the true and right making and touching of them FIrst the wyars that are commonly made both with vs and in forraine countries are of so base and drossie iron not apt nor sufficient to receiue the tenth part of the vertue that fine steele wyar could doe Secondly the ends of the wiars bee for the most part not filed smooth nor fitted euen together vpon the Axis of the flie By meanes whereof the touch of the stone is more dully receiued and the standing of the flie the more vncertain the magneticall force not being in the true axis thereof The reason heere of is this the Magnet giueth his force Secundum mensuram recipientis according to the capacity of that which receiueth it and that euer more after his owne nature which is to haue his force strong in his ends and none at all in the middle if you touch the blade from the middle with either end of the stone the other end of the haft will immediate receiue and shew the contrary quality euen so also will it come to passe if you make proofe with any Magneticall needle although that his force will bee faint and weake in comparison of the other And in your touching you must obserue that in pressing with the stone from the middle of the needle vnto the end as you bring your hand backward to iterate the touch you must lift your hand somewhat high and not bring it backeward close to the needle For that would diminish the strength of the touch But if that end of the needle be also touched with the other end of the stone in manner as aboue I haue rehearsed then shall hee at each end be a great deale the more strong and the contrary fainter forces shall recoile and settle in the middle of the needle where they can nothing at all disturbe the motion thereof CHAP. IX Of the touching with a Laadstone capped and without the cappe BY capping is meant the placing of two peeces of iron handsomely fitted and fastened vpon the two points of the stone for iron for this purpose is better then steele And likewise concerning the the waight that is to bee lifted vp it is better to bee made of soft iron then of steele and the stone will lift more therof as long as there is contiguity but if if the iron and steele be separated from the contiguity of the stone the steele will alwayes carry at the least tenne times more vertue then the iron as is before mentioned Now whether it were best to touch the wiers with a Magnet being thus capped or with the bare stone it selfe some there be that make a question I haue beene tolde by one of great skill and practise that he found by experience the Compasse touched with a capped stone not to receiue his force so well as the other and the party comming vnto me when he was to vndertake a long voyage to haue his compasse touched requested mee in any wise to doe it with the bare stone But yet I thinke it were good that this bee confirmed by more then one mans experience before it be beleeued because by some error he might possibly mistake the matter Sure I am that the capped stone giueth somewhat more vertue in his touch and by all experience that I haue made I finde it to continue as firmely and as long Howbeit I referre mee heerein to the ttiall of others also A man may therefore touch the wiars first with the bare stone then with the same being capped or contrariwise to bee surer of the greater force and yet if any shall imagine the difference of the strength of the touch to be according to the taking vp of iron with the cap or without it he is very greatly deceiued For I haue osten tried them both but neuer could see the touching strength in the needle to be increased halfe a quarter more with the cap then without it whereas I haue alwayes especially if the stone were very good found that the stone wil lift at the least ten times as much iron yea a great deale more and sometimes twenty times with the cap if it be artificially fitted then he is able to doe without it Some who would seeme to be of great skill haue imagined that the best way to adde strength to a needle is with a hammer to giue some forcible strokes to one point of the stone thereby causing litragges as it were or beard to hang downe from it that the needle in his touching taking some part of that with him should haue the stronger touch But they that so suppose deceiue themselues therin for that beard is nothing else but the fine dust of the stone hanging together by vertue thereof which being separated from the stone although it were a right good one is not able any whit at all to turne a needle of it selfe The triall is soone made by this meanes let them take of that beard
of the South of the one to the North of the other But the ends in the one and the other will alwaies flie from those of like denomination as the North end of the one from the North end of the other and the South end of the one from the South end of the other For as much then as all magnets themselues and all magneticall bodies being so placed as they may haue their free motion compose themselues magnetically towards the Poles of the earth it must needs be that it is the true naturall South end of the Magnet or Magneticall needle that pointeth towards the North of the Earth and it is the true naturall North end of the Magnet or Magneticall needle that pointeth towards the South of the Earth because the contrary ends doe affect one an other and each of them doe naturally flie the one end of the one from that end of the other which is of like denomination vnto it selfe for example In this following Diagram of the whole Magnet E. A is supposed to note the true naturall North end thereof and B. the South end This Magnet being placed in a woodden dish swimming in water freely must and will of Magneticall necessitie with his true North end A. settle himself so that A. must point towards the South of the Earth And the South end B. towards the North of the Earth Because all Magnets and all Magneticall bodies do naturally affect the one the contrary end of the other and doe auoide and flie from their ends of like denomination Now for a further consideration of these properties suppose that you will cut of a peece of this Magnet meridionally viz. C. D manifest experience will shew that C which did in nature participate with A. in the entire Magnet E as being both of the true North part thereof now being separated will not abide it In like manner D of the other end of the little one will not abide B of the great one with whom being entire in nature he did participate as being both true Southerly parts of the entire Magnet E And that because the ends of like denomination of any two Magnets doe naturally flie the one from the other CHAP. III. Certaine generall obseruations of the nature and properties of the Loadstone LOadstones of diuers and sundry parts of the world as of Norway Elva Bengala c. haue one and the selfe-same property directiue I meane of shewing the North and South and also the selfe-same points respectiue declining or dipping vnder the Horizon They doe likewise agree in their variations and each one will draw yron and likewise one another Euery Loadstone of what forme soeuer he be hath either actually or potentially two points the one Northern the other Southerne Actually if either by casualty if it so fall out or by industry the stone be so fashioned that those two opposite points be eminent or perspicuous therein Potentially if that either the stone be flat and but thin in the dimension of North and South though broad otherwise for so shall the vertue of the stone be dispersed to the extreame parts thereof in the edges round about or if it haue the two opposite points in any concauitie then will the stone shew in the eminent border or edge of that concauitie onely a confused dull force and in the concauitie it selfe very little or nothing at all That stone is well proportioned for touching which resembleth an Ouall forme and hath his due points in his ends and is voide of any bunch or concauitie For the generall forme of a stone being good euery concauitie is a diminishing of his force and euery bunch is but a superfluous burden Insomuch that my selfe haue made experience of a stone that of substance was very good and of weight was vpon a three and twenty ounces but of a disordered forme I therefore tooke away twelue ounces from him and yet diminished not one iote of his force And this did I in a stone that was all of like substance But if it be one that is intermingled of diuers substances as many such there are and those easily discerned by their colour you may somtimes take away three quarters and more of his substance without diminishing any thing at all of his vertue For colours most commonly the Iron-like is best very blacke or whitish seldome proues good gray indifferent the more white in any stone so much the worse There are certaine that are of an yron colour mingled with red of which some bee very good some but indifferent By three waies you may proue whether a Magnet be good or not the one is by taking vp yron with the bare stone The other by giuing more or lesse vertue vnto a knife or any such thing to lift yron The third if it will with good strength moue a Magneticall needle a pretty good distance of and readily alter the ends of the needle without touching of them making the North South and the South North The two latter of these doe neuer faile but the first doth diuers times And very certaine it is that whatsoeuer stone doth most strongly impart his force vnto a knife or moue a needle with quicknes the power of lifting vp yron in such a one will mightily be increased with a Cap. For this is generally the nature of all Magnets that if there be 2. of different quantities and equall strength in lifting vp yron the greater will giue the stronger touch and moue a Magneticall needle farther of although the lesser will take vp as much yron or somewhat more than the greater And againe suppose there be a Magnet of a pound weight that being fitly armed will take vp foure pounds of yron and not aboue if you diuide him into very small peeces you shall finde of them being orderly vsed that will lift vp 20 times yea 40 times his owne weight and a great deale more if they be made very small as of three or foure graines weight And yet where the great one will giue a touch vnto a knife for to take vp foure ounces of yron and will moue a Magneticall needle three foote of this little one will not giue a touch vnto a knife to take vp a needle nor moue a Magneticall needle foure inches of that as a Magnet is diminished in substance I meane a Magnet of a regular forme so doth he loose in his vertue of touching and increaseth for his small quantitie in lifting of yron whereby it is manifest that these two properties goe not alwaies ioyntly together in the same proportion and degree And here hence it is that many seeing little Magnets artificially set in rings for to take vp for their quantitie a great peece of yron doe wrongfully imagine that the great one whose particles they are or any other great one should doe the like namely to take vp so many times their owne weights Also very often it is seene that Magnets being of like forme and weight but
yet as truely as that That end which cooled toward the South will draw the true North end of the needle and that end which cooled toward the North will draw the true South end of the needle If so be as yet you will haue another infallible argument doe thus Marke what end draweth the North end of the needle afterward put the new made Magnet into the fire againe and when it hath been glowing for the space of halfe a quarter of an houre take it out and coole it being placed with that marked end toward the North most assuredly that end now will draw the South end of the needle the North end of the needle will shun it which before approached vnto it The reason here of is because the fire hauing abolished all the former Magneticall qualitie of that masse wherewith it was in a contrary position affected in the former cooling now leaueth it apt and fit to receiue any other new impression which presently it taketh againe either regularly if in the cooling it be placed with the ends to the North and South or if it be placed otherwise confusedly by the Magneticall force and vertue of the whole body of the earth by regular and confused this is the meaning Take any lump of earth or any brick-bat ordered in this sort certaine it is that this lumpe of earth or bricke-bat hath some magneticall vertue therein yet so feeble and weake that our sence cannot discerne it because of the vnfitnesse of the forme and the confused dispersion of that weake force through the whole body thereof Then suppose you will bring either of these into an extended ovall forme which is most apt as before I said for any body magneticall to shew his force yet this will helpe it nothing at all of it selfe as you may easily make experience in euery Loadstone For if you take a loadstone of a confused forme it is not inough to bring it into a conuenient ovall except with diligence you reserue the points of the North and South in the two ends thereof for if you leaue the points in the sides you marre it with this ovall forme For the stone will not lightly be of one quarter of the force it was ofbefore For the ovall forme giueth it no vertue but is the fittest for it to shew the vttermost of that strength which of it selfe it had before if you obserue the due points and not otherwise But in this earth and bricke it is not possible to finde the due points in such sort as you may in a Loadstone because of the weaknesse of the magneticall force therein contained And therefore you cannot bring that into a regular ovall forme to haue the due points in the very ends But if you first make it into an ovall forme and by the fire take away the confused magneticall force and all other peruerse qualities thereof that being by nature a magneticall body in his cooling before specified receiueth presently by that vnresistable power of the earth his magneticall vertue according vnto that forme and will regularly haue his due points precisely in the ends without any confusion Iohannes Baptista-Porta Neapolitanus writeth that hee did make triall of the way that Paracelsus hath set downe for to increase the vertue of a magnet namely to heate him red hot in the fire and to quench him in the oyle of Crocus Martis And Baptista Porta saith that hee found it a detestable falshood For saith hee he is so farre from increasing his vertue as that being once red hot he looseth all his own past all recouery But for all this that hee saith I doubt whether Paracelsus be iustly reprooued or not for by mine owne experience I know that the heating of a Loadstone vntill he be red hotte doth weaken a loadstone but taketh not away all his force and in my triall here of I found a very manifest proofe of the magnetisme of the earth which I thought necessary for to insert in this place I haue made this triall of Fragments of magnets of diuers kindes and also of diuers kindes of Iron Mines which are next in degree vnto magnets namely after this sort Heate him in the fire by little and little for feare of breaking vntill he be red hotte then take him out and let him coole then marke with chalke or what you please those parts that respect the North and South and you shall finde those marked places the North and South Poles of the Magnet put him into the fire againe vntill he be red hotte and coole him contrarily and you shall haue the contrary effect Therefore if Baptista Porta did make his triall with a Loadstone very long in forme and chaunced for Master D. Gilberts mistery of the Earths magnetisme was not then reuealed for to coole him in his oyle of Crocus Martis with his ends East and West the axis of the stone being then ouerth wart in the middle it were no maruell if he found no force in the ends And I do not thinke it improbable but that Paracelsus way may doe some good rightly vsed Doctour Gilbert writech that some Iron mine will affect a magneticall needle as it is of it selfe being vnprepared by fire but as yet I neuer could finde any such but this I haue often tried that it being of no manner of magneticall vertue of it selfe no more then a flintstone vnprepared by fire being made red hott and cooled is presently impregnated with very apparant magneticall vertue according to the scituation that hee is cooled in and although you heate and coole him often and diuers waies he will still keepe his vertue according to the scituations of his cooling And some Iron Mines I haue found which being but in this sort prepared haue had as strong force as some naturall magnets haue had It is the goodnesse of the Loadstone ioyned with a fit forme that will shew great force For as a very good forme with base substance can doe but very litle so the substance of the Loadstone bee it neuer so excellent except it haue some conuenient forme is not auaileable For example an excellent loadstone of a pound waight and of a good fashion being vsed artificially may take vp foure pounds of Iron beate it into small pouder and it shall bee of no force to take vp one ounce of Iron yea I am very well assured that halfe an ounce of a Loadstone of good fashion and of like vertue will take vp more then that pound will doe being beaten into powder Whence to adde this by the way it appeareth manifestly that it is a great error of those Phisitions and Surgeons which to remedy ruptures doe prescribe vnto their Patients to take the pouder of a Loadstone inwardly and the small filing of iron mingled in some plaister outwardly supposing that herein the magneticall drawing should doe great wonders Whereas they consider not that the stone being dissolued into powder euery little particle of the dust hath
two points contrarie the one drawing to the other repelling and putting from and so being thus confounded by a contrarie working doth much more harme then good with his magneticall quality As for the astringent and drying properties of the Loadstone I leaue them to the diligent obseruation and iudgment of the skilfull in phisicke But to returne to our purpose and to alledge this also besides the former manifest proofe if the earth were not by nature a magneticall body the afore mentioned peice of earth could not receiue from a Loadstone any magneticall power But most certaine it is and by many vndoubted experiments confirmed that it will euidently receiue magneticall power from a Loadstone therefore it is manifest that the earth is by nature a magneticall body Furthermore as among all the mettals iron doth incomparably more resemble the earth in substance then any other doth it likewise doth more participate with the earth in quality and principally in the magneticall peculiar property hereof as notorious experience declareth yea euery peice of iron Oare being naturally as D. Gilbert sheweth a magnet although of feeble force and all magnets being a kinde of iron Oare is the very cause that onely iron or steele and no other mettall is capable of that vertue namely to haue that reuiued and multiplied by the vicinity of a magnet which at the first in some measure was originall in it selfe as it is aforesaid It is also well knowne that the magnet is a Stone most commonly of inuincible hardnesse nothing inferiour to any iron or steele of the excellentest sort notwithstanding sometimes wee see of them that are nothing but a dry lumpe of earth and yet of those also some stronger in vertue then diuers of the hard stony ones are Which earthly magnets if a man assay to bring it into a fashion by grinding on a grinding stone according to the common vse they will consume into very mudde in the water Now to drawe towards an end of this matter albeit the magneticall vertue be most eminent in the magnet as in the precise and perfect subiect thereof yet is the selfe same quality in a meaner degree euidently to be discerned in euery peice of earth prepared and ordered as is aforesaid yea although it be not cooled with his ends North and South that it may take his magneticall force from the vertue of the earth for if you coole it with his ends but East and West and set two Loadstones in the cooling the one at one end and the other at the other end it will receiue a sensible and apparant magneticall vertue according to those points of the Loadstone that were applied vnto it namely that end which was next the South point of the Loadstone will haue a North properly and that end that was next the North point will haue a South property yea if you set the North part of two loadstones vnto each end both ends of this new made magnet will haue a South property And contrariwise if you apply the South ends of two magnets both his ends will haue a North property And those properties before mentioned will shew themselues to be magneticall because whether end of this new magnet draweth any one end of a magneticall needle the same will chase away the other which is proper only vnto magnets and magnetical bodies After the like sort only by application of two strong loadstones by the space of 24. houres you may alter the points of any base loadstone which you would and make them both North or South as you please so that the loadstone which you would alter be but base in qualitie and not great in substance and that the other be of a reasonable bignes and good strength And this vertue by such application of two loadstones I haue often found effectuall in new bricke lately taken from the kill without any farther putting into the fire at all And although it be against the nature of a loadstone to haue both his ends naturally of one vertue that is to say both of them of a North property or both of them of a South property yet here it is to be vnderstood that it is the forcible violence of the strong ones being applied iointly vnto each end of the weake that doe chase the contrarie property of the weake one into the middle thereof And therefore if you diuide this weak one in the middle then both those ends which being ioyned together were the middle where no loadstone can shew any vertue being now disioyned and become ends will presently shew a contrary property according vnto magneticall nature vnto the other two ends CHAP. II. The ambiguity of the North and South ends of Magnets and Magneticall bodies explained and Doctor Gilbert therein defended THere is not any one errour that breedeth a greater confusion in magneticall knowledge then the mistaking of the right vnderstanding of the true North and South ends aswell in magnets themselues as also in magneticall bodies who soeuer therefore that will take a little paines in the beginning for to vnderstand this well shall free himselfe from many intricate difficulties in this argument which otherwise must needes befall him wherein some hauing limed themselues haue fallen into many errors euery one still begetting another worse then himselfe All those which did write before Doctor Gilbert did name that end of a magnet which being placed in a wooden dish and set to swimme in water would turne and settle it selfe towards the North the North end of the magnet and the other the South end And euen so did they of all Dial-needles Compasses and magneticall bodies But Doctour Gilbert not for any new-fangled innouation or selfe-conceit but vpon good reason and firme demonstration auoucheth and prooueth the contrarie and clearely sheweth that the former vulgar assertion seriously defended tendeth vnto the ouerthrow of all magneticall Philosophie by vndermining as it were the whole frame thereof and yet in common speech the old rule may hold Loquendum cum vulgo sentiendum cum sapientibus For it would seeme a strange speech vnto a Marriner to tell him that his Flower de luce were become the South point of his compasse and yet this assertion is most true and certaine that it is the North end of euery magnet and magneticall body that being placed in a thinne wodden dish in water or any magneticall needle vpon his pinne which setteth it selfe and pointeth vnto the South and it is the South end which pointeth vnto the North. For proofe hereof take these wordes of North and South in whether of the two former significations you please and make triall thereof in any two magnets or any two magneticall bodies so placed that they may freely turne according vnto their natures and you shall alwaies see a naturall inclination of the contrary ends of the one vnto the contrary ends of the other as of the North end of the one vnto the South end of the other and reciprocated
whether it be your North or South end the effect will soone declare The fourth way Hauing an ordinarie Diall with a magneticall needle or a sayling compasse or any magneticall needle standing on a sharpe pinne hold neere thereunto the stone turning it in your hand then will the north end of the needle I meane the end that pointeth to the North respect the true North point of the stone The fift way Also if you touch a common sowing needle the longer the better and put ti through a little peice of corke not bigger then may well beare it vp so that by the meanes thereof it may swimme in a bason of water the same if you offer the stone vnto it will shew the like effect And here it is to be remembred that none other way whatsoeuer will more readily or truely define the magneticall Meridian then this of the needle with corcke in the water And therefore as it is very requisite for many purposes that euery Traueller either by land or especially by sea should alwaies haue if he may an aequinoctiall Diall with him so would I not wish that any of them should be without some sowing needles touched with a good stone which wil both serue the proper vses of sowing without impairing their touch for it is open aire and rust that are the greatest enemies thereof And at any time with a peice of corcke or a drie sticke in the water will shew the magneticall meridian a matter though meane and triuiall in shew yet betweene whiles of so great importance that it may serue to saue very many mens liues A sixth way Also if you prepare a little round Loadstone of a quarter of an inch diameter or there about but it must be a very good one hauing his two poles marked and fitted in such manner that it easily turne about in a little frame according vnto this picture The like also in his sort will come to passe if you hang a small declinatorie Needle in a frame in this manner Then by mouing it in his frame all ouer the stone the North pole of this will finde the South of the other And likewise will the South the North of the great one For it is not in outward shew between one magnet and another as it is betweene a magnet and a magneticall needle the contrarie ends of the magnet will couet in their motion to meete together but the end of the needle which turneth North will come vnto the North of the stone For in very truth it is the South point of the needle euen as the magnet it selfe being placed in a woodden dish in water will turne with his North end vnto the South and with his South end dish and all towards the North as it is largely declared in the second Chapter of this booke The like effect will also follow if you hang as aforesaid a small magnet in the middle by a small silke thread that it may freely turne without impediment according vnto his owne nature But this property it will shew quicker or slower according vnto the goodnesse of the substance and fitnesse of the forme The best forme for this purpose is the extended ovall hauing his poles precisely in his ends If his poles be some pretty distance the one end towards the East of the stone and the other asmuch towards the West this stone in his length will not point vnto the magneticall North and South as otherwise he would but vnto some other point of the Horizon yea following this experiment in this sort you may make him stand vnto any point of the Compasse onely you ought to abridge the stone in his length that he may come somewhat neerer vnto a circuler forme that so his diameter of North and South being through the magnetisme of the earth the cause of this motion may be so much the longer in comparison of the Masse of the stone and consequently more effectuall After the like manner you may so touch the wiers of a Compasse that the Flower de luce of the flie shall stand vnto what point of the Horizon you please although the Diameter of the wiers doe still remaine fixed vnder the Flower de luce and the South point of the Carde Finally to conclude this point with a magneticall delight if you touch two sowing needles in a contrary sort that is the point of the one northerly and of the other Southerly and set them with their corckes the one at the one side of a bason of water and the other at the other you shall see them as quickned with vitall spirit euen so to moue the one end towards the other at the first faire and softly but when they draw neere they will rush together as it were with a kinde of violence the point of the one striking precisely at the point of the other you must place the needle whose point is touched for the North on the South side of of the bason and the other on the other side Otherwise the heads and not the points will runne together a thing farre more worthy of admiration then all the selfe moouers of any Daedalus or Architas Tarentinus and more strange to behold then the connexion of Iron rings combined by vertue magneticall whereat S. Augustine so much and that iustly did wonder CHAP. V. The manner of capping both with single and double cappes and the nature of them THe stone being brought vnto his perfect forme you must haue a mould made of Iron of the very same proportion in euery respect and equall in all his dimensions then setting the stone aside let your workeman frame fashion his cappes and fit them vpon this mould as if it were the stone thus shall you be sure to preserue your magnet from many dangers very incident vnto rude handling And hauing so done you may set them on the stone it selfe amending any small faults without endangering the stone either with bruisings or knocks For the thicknesse and largenesse of the cappes there can bee no generall rule prescribed but it must be left vnto the triall and ingenious dexterity of the workeman as also for the handsome fastening either by soadering or riuetting of them with lattin plates to the Caps to keepe them in their places firme and steddy according as you see in this picture of a stone armed with single Cappes Now therefore in this position both ends of the Magnet being applied vnto the two ends of the iron these two contrary forces striue in this peece of iron the North to repell the South and the South the North so that each force is driuen neerer his owne end and becommeth there so much the stronger then otherwise it would be For proofe whereof take a little narrow square peece of iron of the length of the capped stone and ioyned in the middest with Copper after this sort A. is supposed to be a long square or a square-like peece of iron in length fitting the two double caps
of a Loadstone B. a long square peece the ends iron the middle copper C. hath a lesse space of copper and D. least of all If you apply the Loadstone vnto A he will hold A very strongly but if you put any of the other three peeces vnder A that it may touch any of them hee will not by any meanes lift it vp If you apply the Loadstone vnto B he will take it vp very weakly and C somewhat more strongly but D strongest of all these three yet not comparable to the strength wherewith hee taketh vp A. Againe although the Loadstone taketh vp B but weakly yet if you place B vpon A he will take them both very strongly yea more place B vpon C these two vpon D all three vpon A apply the Loadstone vnto B being the vppermost and he will lift them all vp very easily The cause hereof is when a Loadstone with his double cappe is placed vpon A the force of both ends striuing in that peece of iron paralel-wise vnto the Axis of the stone the North and South forces are driuen more closely vnto their proper ends But in B because of the intermediate copper there can be no such close driuing of his forces into their proper ends as was in A and therefore the Loadstone lifteth vp B but only as if his two ends were two little loose peeces of iron hanging in the aire and the intermediate copper a burthen vpon them But placing B vpon A A in the manner as it were of a bridge ioyneth the two ends together into their former combats and the two ends of B forasmuch as they are but as it were two loose peeces of iron hanging in the aire the two forces of the Loadstone North and South distinctly and seuerally passe thorow them downwards into A which it could not doe if it had beene one entire peece of iron and so all those foure peeces being placed one vpon another so that A be vndermost whether directly or sidewise the Loadstone will easily lift them all vp and not otherwise When a Loadstone lifteth vp iron at one end onely the vertue of the stone is infused into the whole body downward of that iron if it be not very long But when by the meanes of the double cappes both ends doe lift iron ioyntly together he infuseth very small force downeward into the body of the iron that it lifteth vp for the forces of the both ends are so striuing in a collaterall line of the iron paralell vnto the Axis of the stone that whereas a good Magnet lifting vp at one end will extend his vertue downewards twelue or fourteene inches in applying both ends vnto the iron by the meanes of the double caps hee will not extend his force downeward the distance of one inch nor with any strength the distance of halfe an inch as in this former example Pliny in his naturall historie writeth that Dinocrates that famous Architect builder of Alexandria at Ptolemies commandement began to vault a Temple with Magnets that there might seeme to hang in the aire the image of his sister Arsinoe made of iron for that purpose but both Dinocrates and Ptolemie dying in the meane space that enterprise ceased Neither indeed if they both had liued could it euer haue come to passe by that means by reason of two impossibilities The one is that by the force of the Loadstones nothing can so hang in the aire but that it either must touch the stone it selfe or some other intermediate substance betweene it and the stone that barreth it from comming to the stone it selfe For example lay two or three needles vpon a smooth table put a siluer or pewter plate vpon them and vpon the plate a Loadstone then lift vp the plate aloft with the Loadstone lying still vpon it and you shall see the needles hanging indeed in the aire endlong and if you moue the stone about the plate following still vnderneath but euermore touching the plate which is the intermediate body that keepeth them from comming to touch the stone which otherwise by their naturall inclination very speedily they would doe But as for that image of Arsinoe how had it beene possible for it to haue touched at once mediately or immediately so great a number of Magnets whereof the pretended vault must needs haue consisted The other is that such a multitude of Magnets would nothing but confound the one the others forces so that one of them alone being solitarie and seuered from his company might shew more force then al that insociable societie could doe each one hindering the efficacie of the other Much like a teeme of many horses where euery one drawing his sundry way might soone with disordered stretching tire himselfe and his fellowes but neuer moue the loade one iot from the place Insomuch as one and possibly the worst would doe more good alone where hee might orderly and freely vse his owne strength then hee and all the many of them could doe being ioyned together in vicinitie of bodies but extremely distracted through contrarietie of courses The only way to performe such a matter if it were worth a doing would be to prepare one mightie great Loadstone of excellent goodnesse which hauing his due proportion after an extended ouall forme should be sitted with double cappes and so placed in the roofe of a building that his Axis be paralell to the Horizon in this sort out of all doubt a faire large image might bee held vp very strongly by such a Magnet let the stuffe or substance thereof be whatsoeuer howbeit the lighter the better so that there be fastened vnto the vppermost part of the Image a small peece of iron accordingly prepared and placed for the two prominent ends of the double cappes of the stone to lay hold thereon But enough hereof In the capping of Magnets this generall rule is to be obserued that they ought to be made of the finest and softest iron and not of steele the waight also which the Magnet taketh vp should be of the like iron and not of steele as aforesaid For although steele retaineth at the least ten times as much vertue as iron when it is once separated from the stone can doe yet as long as there is any contiguitie betweene the stone and them hee holdeth iron more strongly then steele Both which differences in either of them by manifest experience are certaine and seeme to proceede of notable fastnesse or closenesse in the steele aboue the iron by meanes whereof the magneticall vertue doth longer and more forcibly continue in that then in this euen as fire more mightily possesseth and for a greater space abideth in stone or any such firme or solid matter then in wood or straw or the like thinne and hollow substances and therefore those compasse-makers that make the wiers of their flies for sailing compasses of meere iron ought not by any meanes to be suffered for to gaine two pence in a compasse and
to a Masons trade they will haue 40 points twenty North and as many South and will worke the like effect in drawing yron as to vse the former grosse similitude if a teeme of horses were set in their traces contrary the one to the other the one to pull one way the other another As for the Turkes Mahomet hanging in the ayer with his yron chest it is a most grosse vntruth and vtterly impossible is it for any thing so to hange in the ayer by any Magneticall power but that either it must touch the stone it selfe or else some intermediate body that hindreth it from comming to the stone like as before I haue shewed or else some stay below to keepe it from ascending as some small wier that may scantly bee seene or perceiued CHAP. VII Of the variation of the Magneticall Needle with the Appurtenances therevnto belonging THE variation of the Magneticall Needle being aptly fitted and placed vpon his pinne is nothing else but the swaruing of the pointing thereof in the Horizon from the meridian line there the portion of the Horizon intercepted betweene the true Meridian line and this pointing sheweth of what quantitie the variation is and giueth it his name to wit which way it lyeth either Easterly or Westerly and it is obserued by either end of the needle as you please In times past men obserued onely by the North end of the needle because they vnderstood not that the Loadstone hath a South vertue as well as a North And therefore did touch their needles and wyars of their compasses alwaies for the North onely leauing those ends of the wyars bare that they might be refreshed with a new touch at any time afterwards but the other ends they couered not knowing that they were also apt to receiue as forcible a vertue from the Loadstone for the South as the other for the North. For the right vnderstanding of the variation with his necessary dependants wee must vse the meanes of two circles The one of them I will call the Magneticall Almicanter The other is already knowne by the name of the Magneticall Meridian This Magneticall Almicanter is a circle paralell vnto the Horizon whose center is the verticall point and is described by the distance betweene the verticall point and the neerer Pole of the earth The true Magneticall Pole is the pole of the earth The magneticall respectiue Pole or which is all one the Pole of the Magneticall Meridian is a point in the Magneticall almicanter distant Easterly or Westerly from the true pole as many degrees in that almicanter as the variation of that place containeth in the Horizon but alwaies it is in the contrary part of the true Meridian that is if the variation of the South point of the needle be Easterly the respectiue pole is Westerly but if you obserue with the North end of the needle the respectiue pole and the variation are both one way in all our Northerne Climates If the variation of the South point of the needle bee Westerly then is the respectiue pole so many degrees in the said almicanter Easterly and therefore alwaies of the same height with the true pole aboue the Horizon For since all great Circles of the globe doe necessarily cut one another in two points into two equall parts these two therefore must needes doe euen so in the Zenith and Nadir by their very definitions So that these two points the Zenith and Nadir are alwaies alike common vnto them both aswell vnto the true as vnto the Magneticall Meridian Where-hence it followeth necessarily that alwaies the one halfe of the magneticall meridian is on the East-side and the other on the West side of the true meridian the common Zenith and Nadir euermore keeping their equall distances from the Poles of the one of them as they doe from the other For example Suppose the common Zenith to be in the Aequator you sayling East or West as long as there is no variation there is no magneticall meridian there are no magneticall Poles but those of the world But as soone as sayling still vnder the line you doe finde a variation it is the magneticall meridian that by his swaruing from the true meridian of the world in the Horizon sheweth the quantity of the variation and giueth it also the denomination of Easterly or Westerly and his axis is the line of variation But supposing the common Zenith to be in any paralel betweene the Aequator and the Pole then is it not the axis but some other Diameter of the magneticall meridian which sheweth the variation in the Horizon And the magneticall meridian euermore cutteth iust so many degrees of the magneticall almicanter on the one side of the true meridian as the same Magneticall Pole is distant in the same almicanter on the other side of the true Meridian from the Pole of the World And this is to be vnderstood in correspondent manner as well of the South Hemisphere as of the North. The respectiue Magneticall meridian where any variation is is a circle that passeth by the verticall point and the Nadir and both the respectiue Poles crossing the Horizon at right angles in the points of variation of which circle the line of variation is a Diameter but where there is no variation the true and Magneticall meridian are both one the selfe same and so in like manner are their Diameters Those circles and poles are tearmed respectiue because that in euery place where any variation is the Magneticall needle doth respect them as well in the property of direction as in that of declination or inclination For thus also very well it may bee tearmed By the property of direction I doe meane with Doctour Gilbert the Horizontall motion of the Magneticall needle By the declination or inclination I meane the descending and as it were the sinking motion of the neede vnder the Horizon in his proper Azimath or Magneticall meridian But if there be no variation the needle alwaies pointeth vnto the true Meridian of the earth and towards the Poles therof in both those properties The true Poles of the earth which are those two points equally distant from each part of the Aequinoctiall of the earth are alwaies the selfe same The respectiue Poles alter with euery Horizon where there is any variation but neuer out of the aforenamed almicanter of that place The causes of the differences of the respectiue Poles and Meridians from the true Poles and meridians and so of all variations are onely two The chiefe and most generall is the vastenesse of the Ocean sea by moistnesse whereof the Magneticall collaterall force of so much earth as it couereth is much hindered and dulled And by that meanes the next great Continent hath more power ouer the correspondent end of the Magneticall needle then otherwise it could haue if all were alike one entire Continent and therefore causeth the directiue property of the needle somewhat to swarue towards that way
from the stone with a sticke and lay it vpon the end of a needle not touched and they shall finde in it no force at all nay it is a hurt vnto the needle For it giueth a superfluous burthen for a small time and cannot but incumber his action by reason that euery one of those little parcels of dust though beaten out at one end hath also for his small quantity both a North and South vertue And therefore marreth as much as it maketh at either end of the needle The proofe heereof is manifest if you put off that dust or beard vpon a paper and hold a Magnet therunder for as you turne towards the paper the North or South of the stone so will euery one of those particles in like sort turne it selfe shewing thereby a double nature CHAP. X. Of the fashioning of the compasse needle THe Compasse needle being the most admirable and vsefull instrument of the whole world is both amongst ours and other nations for the most part so bungerly and absurdly contriued as nothing more And therefore entreating now of the nature and vse of the Magnet I haue thought good also to employ my best endeauour to aduance this noblle instrument towards his highest perfection being the principall thing by which the worthy effect of the Magnet is made most profitable vnto mankinde Heerein fiue things are to be considered the substance that it is made of the forme the waight the capitell and the pin it standeth vpon The substance in any wise ought to bee pure steele and not iron For most assuredly steele will take at the least tenne times more vertue then iron can doe but especially if it hath his right temper And that is this Heat it in the fire vntill it be past red hot that it be whitish hot and qnench it in cold water suddenly So is it brickle in a manner as glasse it selfe and is at that time incapable of the vertue of the Loadstone Then must you laying it vpon a plaine table warily rubbe with fine sand all the blacke cullour from it if before you put it into the fire you annoynt it with soape it will scale white of it selfe then heat a barre of iron well neere red hot and holding one end of the needle with a small paire of tongs lay the other end vpon the hot barre and presently you shall see that end turne from white to a yellowish and after to a blewish cullour then take that end with your tongs and doe thlike vnto the other thrusting it forward vpon the barre vntill the cullour of the whole needle become blewish then throw it on a table and let coole of it selfe and so is he of the excellentest temper and most capable to receiue the greatest power from the Magnet If this seeme too curious especially for some fashions of needles then vse but the hammer hardening as workmen call it which is well neere as good As concerning the forme diuers men are of diuers mindes some vse a kind of square one others a loop I meane an extended ouall forme and this is most common But now a dayes a narrow straight place being somewhat broader in the middle is in great request Of these three I holde the loope or ouall forme if it bee well made to bee the best which is that if it be of steele his ends be welded together hauing a lattin narrow plate issuing from the capitell vnto the middle of the two sides of the Loope and there riuetted and riuetting if it bee handsomely shouldered in by the workman is better then soadering because hauing fitted the lattin plate bearing the capitell vnto the Loope you may first put your Loope into his temper and then riuet this vnto him afterwards which otherwise would bee marred in the fire and the wide Loope is better then the narrow or the straight plate and that for two reasons The one is hecause as in a Magnet it selfe the force that is in the whole body sheweth it selfe most strongly in his two poles euen so this being a Magneticall body doth the like in his ends which are his poles and the sides of a wide compassed Loope being longer then of a narrower of the same length in the Axis must needes containe so much the more vertue the other reason is because it supposeth the flie in his circular motion more equally ballanced then the other and therefore were it not for some other inconueniences a true circle were best of all which is that except you marke the two places that you would haue for the North and Souch very curiously you shall neuer giue him the right touch yea very exceeding hardly although you doe marke them and also the lattin stay that holdeth the capitell would bee exceding long and a superfluous burden but the very best forme of all as I take it in all respects is this a true circle hauing his Axis going out beyond the circle at each end narrow and narrower vnto a reasonable sharpe point and being pure steele as the circle it selfe is haning in the middest a conuenient receptacle to place the capitell in This circle must haue foure very small holes drilled through it equally distant each from other for the foure cardinall points and in both the two poynts that issue without the circle being for North and South of equall distance betweene the circle and the end of the poynt two moe if it be a large one otherwise one is enough according vnto this picture following And this needle is most fit to be vsed for the obseruation of the variation alone without any flie as I will shew at the latter end of this Treatise Whensoeuer you wil set this needle vnto the fly you must put the capitell through the center of the flie very precisely and placing the points of the Diameter where you will haue them thrust little small pins through the vpper face of the flie and those small holes in the needle the heads of the pinnes will shew you if the flie bee larger then your needle at what poynt your needle standeth and bowing the body of your pinnes being thrust through those little holes close to the card below will keep it steddy at that place and from warping also And so foure pins at the foure cardinall points will serue the turne Againe if you please for to place this needle vpon the vpper face of the Card according vnto Steuinius it is no more but to haue the capitell loose thrust thorough the center in the bottome of the flie and the needle placed and fastened on the top or vpper face of the carde But if you will haue a Magneticall needle to serue onely for one size of a flie the best way is insteed of the two pinnes in the ends of the Axis to haue a couple of little halfe staples and a Flower de luce on one of them as you see in the Loope riuetted there That in turning about the needle they may