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Chambers, Ephraim, 1680 (ca.)-1740 / Cyclopædia, or, An universal dictionary of arts and sciences : containing the definitions of the terms, and accounts of the things signify'd thereby, in the several arts, both liberal and mechanical, and the several sciences, human and divine : the figures, kinds, properties, productions, preparations, and uses, of things natural and artificial : the rise, progress, and state of things ecclesiastical, civil, military, and commercial : with the several systems, sects, opinions, &c : among philosophers, divines, mathematicians, physicians, antiquaries, criticks, &c : the whole intended as a course of antient and modern learning
(1728)

M - mapparius,   pp. 478-497 PDF (19.4 MB)


Page 485


( 485 )
lefen'd, by the various Application of Iron, or another
Loadilone to it. (x5.) A flrong Magnet at the leafd
diftance from a IeCTer or a weaker, cannot draw to it a
piece of Iron adhering aaually to fuch letfer 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 fironger Loadfcone.  (16.) In thefe
Northern Parts of the World, the South Pole of a Load-
flone 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 Loadflone, either
as to its Attrac~ive or Direffive Quality. Mr Boyle found
it true in Glaies fealed hermetically i and Glafs is a
Body, as impervious as mofi are, to any Effiuvia.
(iS.) The Power or Virtue of a Loadflone may be im-
paired by lying long in a wrong Pofition, as alfo by
Ruff, Wet, Wc. and may be quite deflroy'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, Lcc
generally, quite lofe its Direcive Vertue; but always
have it much diminidh'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
firait, the Virtue will not be defiroy'd in thofe parts; tho
it will in all the ref+. This was fir1' obferv'd by Grimaldi
and dela Hire; and is confirm'd by the Experiments of
Mr. Derbam; who adds further, that tho coyling or
bending the Wire as above, would always deflroy its Vir-
tue by Day, yet it would not do it in the Evening.
(20.) The Sphere of the Adfivity of Magnets is greater
and Iefs at different times: in particular, that preferv'd in
the Repofitory of the Royal Society will keep a Key or
other Body fufpended to another, Sometimes, at the height
of 8 or io 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. Grabam.
See Variation. (1z.) By twifling a piece of Wire touch'd
with a Magnet, its Virtue is exceedingly diminifh'd, and
fometimes fo diforder'd and confus'd, that in fome parts
it will attra.r, and at others repel; and even in fome
places one fide of the Wire feems to be attraded, and the
other fide repell'd by one and the fame Pole of the Stone.
(a a.) A piece of Wire that has been touch'd, being fplit
or cleft into two; 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 uppermoPc, caufes a great Altera-
tion in its Tendency or Averfion to the Poles of the Mag-
wet. (a 3.) 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.
(o4.) 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 Poles ( 5.) If a Mag
xet 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 Phx-
nomena) found he could prefently change the Poles of a
fmall Fragment of a Loadcdonej 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, Uic. will, while warm, attrac thin
p Filings or Chips of Iron, Steel, kic. but not when cold;
tho there are not wanting fome Inflances of their retain-
ing the Virtue when quite cold. (28.) The Iron Bars of
Windows, 0c. which have a long time flood in an ere&
Pofition, grow permanently Magnetical; the lower Ends
of fuch Bars being the North Pole, and the upper the
Southern. (29.) A Bar of Iron that has not flood long in an
ere& poflure, if it be only held perpendicularly, will be-
come M agnetical; and its lower End the North Pole; as
appears from its attrafing the South Pole of a Needle:
but then this Virtue is tranfient, and by inverting the
Bar, the Poles will fhift their places. In order therefore
to render the Quality permanent in an Iron Bar, it mud
continue a long time in a proper Pofition. But the Fire
will produce th' Effe& in a 1hort time: for as it will
immediately deprive a Loadflone of its Attrafive Vir-
tue ; fo, it foon gives a Verticity to a Bar of Iron, if being
heated red hot, it be cool'd in an erea poflure, or di-
reftly North and South. Nay, Tongs and Fire-forks, by
being often heated and fet to cool again in a poiture
M A G
nearly ere&s, have gain'd thig Magnetical Property.
(30.) Mr. Boyle found, that by heating a piece of Englhp
Oker red hot, and placing it to cool in a proper pofture,
it manifefily acquired a Magnetic Virtue. And an excel-
lent Magnet of the fame Ingenious GentlemAnds having
lain near a Year in in inconvenient potlure, had its Vir-
tue furprizingly impair'd j as if it had been by Fite.
(31.) A Needle well touch'd, 'tis known, will point
North and South: if it have one contrary Touch of the
fame Stone, it will be deprived of its Faculty ; and by
another fich 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
then hammer'd at the two Ends; its Virtue will be de-
flroy'd by two or three fmart Blows on the middle. (33.)
By drawing the Back of a Knife, or long piece of Steel;
Wire, Ec. leifurely over the Pole of a Loadflone; carry-
ing the Motion from the middle of the Stone to the Pole ;
the Knife or Wire does accordingly attraa 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 ir attraa1s.
(3 4.) Either a Magnet or a piece 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 attradls the
Magnet as much as it is attracted by it; A dion and Re-
a=ion being always equal. In this Experiment, if the
Magnet be fet afloat, it will dired its two Poles to
the Poles of the World. (35.) A Knife, &c. touch'd
with a Magnet, acquires a greater or lefs degree of Vir-
tue, according to the part it is touch'd on. It receives
the firongeff 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 polrefflon
of a trong attraffive Power, be retouch'd in a contrary
Diredion, viz, by drawing it from the Point towards the
Handle over the fame Pole, it immediately lofes all its
Virtue. Lafily, A Magnet ads with equal force in vacuo,
and in the open Air.
The Dodrine of the Magnet, or the Laws of Magnetifin
Mr. Wbihfon lays down in the following Propofitions.
I. The Loadflone has both an attradive and a diredive
Power united together; whereas Iron touch'd by it has
only the former: i. e. the Loadflone not only attrads
Needles or Filings of Steel, but diredts them to certain
different Angles, with refpedt to its own Surface and Axis t
whereas Iron touch'd with it, does little or nothing more
than attrac them; fill fuffering them to lie along or dando
perpendicular to its Surface and Edges in all places; w ith-
out any fuch fpecial Direffion.
II. Neither the fironged nor the largefl Loadflones give
a better diredive 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 Attraffive andt
a Diredive one j neither of 'em depend on, or are any
Argument of the Stre'ngth of the ot her.
III. The Attradive Power of Loadolohies and of Iron,
will greatly increafe or diminifh the Weight of Needles
on the Ballance; nay, will overcome thatt Weight, and
fuflain other additional Weights too: while the diredfive
Power has much fmaller effed. Ga/fendus indeed, as well
as -Merfennus and Dr. Gilbert, maintain it has none at all ;
but by a Miflake; for Mr. WbitJon found fromn repeated
qi rials on large Needles, that after the Touch they
weigh'd lefs than before. One of 4584 -v' Grains loft 2  1
Grains by the Touch ; and another of 65726 Grains
weight, no lefs than 14 Grains.
IV. 'Tis probable that Iron confiRs almofl wholly of
the Attradfive Particles ; and the Loadfone of the At-
tradfive and Direffive together ; mix'd probably with other
heterogeneous Matter; as hiving never been purg'd by
the Fire, which Iron has: And hence may arif the rea-
fon why Iron, after it has been touch'd, will lift up much
greater Weights than the Loadfone that touch'd it.
V. The Quantity and Diredion of Magnetic Powers,
communicated to Needles, is not properly, after ftch
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 Terreffrial
Load Rone, whofe Influence alone thofe Needles are af-
terwards fubjea to, and direfted by: fo that all fuch
Needless if good, move with the fame Strength and
Point to the tame Angle; what Loadfdone foever (pro-
vided it be good) they were excited by. Nor does the
Touch feem to do much more in Masetical, than Attri-
tion in Elearical Cafes; i. e. it ferves to rub off fome
obtiruding Particles that adhere to the Surftce of the
Steel, and open the Pores of the Bodies touched, and fo
make way for the Entrance and Exit of fuch Effluvia as
occafion or affix the Powers we are fpeaking of. Hence
Hhhhhh                          by
MAO


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