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leffen'd, by the various Application of Iron, or another Loadftone to it. (15.) A ftrong Magnet at the leaft distance from a leffer or a weaker, cannot draw to it a piece of Iron adhering actually to luch letter or weaker Stone ; but if it come to touch it, it can draw it from the other: But a weaker Magnet, or even a little piece of Iron, can draw away or feparate a piece of Iron contiguous to a greater or flronger Loadftone. (i<S.) In thefe Northern Parts of the World, the South Pole of a Load- Ilone will raife up more Iron than the North Pole. (17.; A Plate of Iron only, but no other Body inter- pofed, can impede the Operation of the Loadftone, either as to its Attractive or Directive Quality. Mr Boyle found it true in Glaffes fealed hermetically 5 and Glafs is a Body, as impervious as mod are, to any Effluvia; (18.) The Power or Virtue of a Loadftone may be im- paired by lying long in a wrong Pofition, as alfo by Ruft, Wet, He. and may be quite deftroy'd by Fire. (19.) A piece of Iron Wire well touch'd, will, upon being bent round in a Ring, or coyl'd round on a Stick, He. generally, quite lofe its Directive Vertue ; but always have it much diminifh'd : and yet if the whole length of the Wire were not entirely bent, fo that the Ends of it, tho but for the length of one tenth of an Inch, were left ftrair, the Virtue will not be deftroy'd in thofe parts ; tho it will in all the reft. This was firft obferv'd by GrimaUi and delaHire; and is confirm 'd by the Experiments of Mr. Verbam ; who adds further, that tho coyling or bending the Wire as above, would always deftroy its Vir- tue by Day, yet it would not do it in the Evening. (20.) The Sphere of the Activity of Magnets is greater and lefs at different times: in particular, that preferv'd in the Repository of the Royal Society will keep a Key or other Body fufpended to another, fumetimes,at the height of 8 or 10 feet ; and at others, not above 4 feet. To which we may add, that the Variation of the Magnetical Nee- dle from the Meridian, varies at various Times of the Day ; as appears from fome new Experiments of Mr. Graham. See Variation. (21.) By twilling apiece of Wire touch'd with a Magnet, its Virtue is exceedingly dimini/h'd, and fometimes fo diforder'd and confus'd, that in fome parts it will attract, and at others repel ; and even in fome places one fide of the Wire feems to be attracted, and the other fiderepell'd by one and the fame Pole of the Stone. (22.) A piece of Wire that has been touch'd, being fplit or cleft into two 5 the Poles are fometimes chang'd ; as in a cleft Magnet ; the North becoming the; South, and the South the North : And yet fometimes one half of the Wire will retain its former Poles, and the other half have 'em changed. To which it may be added, that laying one or other fide of the half uppermoft, caufes a great Altera- tion in its Tendency or Averfion to the Poles of the Mag- net. (23.) A Wire being touch'd from End to End with the fame Pole of the Magnet, the End whereat you begin will always turn contrary to the Pole which touch'd it : If it be again touch'd the fame way with the other Pole of the Magnet, it will then be turn'd the contrary way. (21.) If a piece of Wire be touch'd in the middle with only one Pole of the Magnet, without moving it backwards or forwards, in that place will be the Pole of the Wire ; and the two Ends will be the other Pole. (25.) If a Mag- net be heated red hot ; and again cool'd either with its South Pole towards the North in a horizontal Pofition, or with its South Pole downwards in a perpendicular Po- fition ; its Poles will be changed. (26.) Mr. Boyle (to whom we are indebted for the following Magnetical Phe- nomena) found he could prefently change the Poles of a fmall Fragment of a Loadftone, by applying them to the oppofite vigorous ones of a large Magnet. (27.) Hard Iron Tools well temper'd, when heated by a brisk Attrition, as filing, turning, He. will, while warm, attract thin Filings or Chips of Iron, Steel, He. but not when cold ; tho there are not wanting fome lnftances of their retain- ing the Virtue when quite cold. (28.) The Iron Bars of Windows, He. which have a long time flood in an erect Pofition, grow permanently Magnetical ; the lower Ends of fuch Bars being the Is'orth Pole, and the upper the Southern. (29.) A Bar of Iron that has not flood long in an erect pofture, if it be only held perpendicularly, will be- come Magnetical ; and its lower End the North Pole ; as appears from its attracting the South Pole of a Needle : but then this Virtue is tranfient, and by inverting the Bar, the Poles will fliift their places. In order therefore to render the Quality permanent in an Iron Bar, it muft continue a long time in a proper Pofition. But the Fire will produce the Effect in a fhort time : for as it will immediately deprive a Loadftone of its Attractive Vir- tue ; fo, it loon gives a Verticity to a Bar of Iron, if being heated red hot, it be cool'd in an erect pofture, or di- rectly North and South. Nay, Tongs and Fire-forks, by being often heated and fet to cool again in a pofture
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near y erect have gain'd this Magnetical Property. (3c.; Mr. Boyle found, that by heating a piece of Emli/b Oker red hot, and placing it to cool in a proper pofture: it mamfeftly acquired a Magnetic Virtue. And an excel- lent Magnet of the fame Ingenious Gentleman's having lain near a Year in an inconvenient pofture, had its Vir- tue furprizmgly impair'd ; as if it had been by Fite. (31.) A Needle well touch'd, 'tis known, will point North and South : if .t have one contrary Touch of the lame Stone, it will be deprived of its Faculty ; and bv another fuch Touch will have its Poles quite changed (32.) A Bar of Iron that has gain'd a Verticity by being heated red-hot and cool'd again, North and South and thenhammer'd at the two Ends; its Virtue will be de- ftroy'd by two or three fmart Blows on the middle. (-, ) By drawing the Back of a Knife, or long piece of Steel Wire, He leifurely over the Pole of a Loadftone ; carry-' mg the Motion from the middle of the Stone to the Pole ; the Knife or Wire does accordingly attract one End of a Needle : but if the Knife or Wire be pafs'd from the faid Pole to the middle of the Stone, it will repel that End of the Needle, which in the other Cafe it attracts. (34.) Either a Magnet or apiece of Iron being laid on a" piece of Cork, fo as to fwim freely in Water ; it will be found, that which foever of the two is held in the hand the other will be drawn to it : fo that Iron attrafts the Magneto much as it is attracted by it; Action and Re- aflion being always equal. In this Experiment, if the Magnet be fet afloat, it will direct its two Poles to the Poles of the World. (35.) A Knife, He. touch'd mth a. Magjtet, acquires a greater or lefs degree of Vir- tue, according to the part it is touch'd on. It receives the ftrongeft Touch, when it is drawn leifurely from the Handle towards the Point over one of the Poles - And if the fame Knife thus touch'd, and thus in poffeffioii of a ftrong attractive Power, be retouch'd in a contrary Direction, viz. by drawing it from the Point towards the Handle over the fame Pole, it immediately lofes all its Virtue. Laftly, A Magnet afts with equal force in Vacuo and in the open Air.
The DoBrine of the Magnet, or tie Lams of Magnetifm Mr. Whifton lays down in the following Propositions.
I. The Loadftone has both an attractive and a directive Power united together ; whereas Iron touch'd by it has only the former : i. e. the Loadftone not only attracts Needles or Filings of Steel, but direfls them to certain different Angles, with refpect to its own Surface and Axis : whereas Iron touch'd with it, does little or nothing more than attract them ; ftill fuffering them to lie along or ftaud perpendicular to its Surfiice and Edges in all places ; with- out any fuch fpecial Direction.
II. Neither the ftrongeft nor the largeft Loadftones give abetter directive Touch to Needles, than thofe of a lefs Size or Virtue : to which it may be added, that whereas there are two Qualities in all Magnets, an Attractive and a Directive one ; neither of 'em depend on, or are any Argument of the Strength of the other.
III. The Attractive Power of Loadftones and of Iron will greatly increafe or diminifh the Weight of Needles on the Ballance ; nay, will overcome that Weight, and fuftain other additional Weights too : while the directive Power has much fmaller effect. Gaffettdus indeed, as well as Merfemms and Dr. Gilbert, maintain it has none at all ; but by a Miflake ; for Mr. Whifiim found from repeated J rials on large Needles, that after the Touch they weigh'd lefs than before. Oneof4 5 84f Grains loft 2 | Grains by the Touch ; and another of 6^16 Grains weight, no lefs than 14 Grains.
IV. 'Tis probable that Iron confifts almoft wholly of the Attractive Particles ; and the Loadftone of the At- tractive and Directive together ; mix'd probably with other heterogeneous Matter ; as having never been purg'd by the Fire, which Iron has : And hence may arife the rea- fon why Iron, after it has been touch'd, will lift up much, greater Weights than the Loadftone that touch'd it.
V. The Quantity and Direction of Magnetic Powers, communicated to Needles, is not properly, after fuch Communication, owing to the Magnet which gave the Touch ; but to the Goodnefs of the Steel that receives it, and to the Strength and Pofition of the Terreftrial Loadftone, whofe Influence alone thofe Needles are af- terwards fubject to, and directed by : fo that all fuch Needles, if good, move with the fame Strength and Point to the fame Angle; what Loadftone foever (pro- vided it be good) they were excited by. Nor does the Touch feem to do much more in Magnetical, than Attri- tion in Electrical Cafes ; i. e. it fcrves to rub off fome obstructing Particles that adhere to the Surface of the Steel, and open the Pores of the Bodies touched and {o make way for the Entrance and Exit of fuch Effluvia as occasion or afiift the Powers we are fpenkine of. Hence
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