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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

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

Page 487

1MA O. -
dius is alfo an Arc of a great Circle of about 44 Degr(
XXI. The refpeaive 'Motion of the internal Mag
or the Velocity, v. g. of its North-Pole, appears to
2.7 Deg. o Min. in i44 Degrees, i. e. one Degree in
Years; fo that it makes an entire Revolution in I
Hence as the Number of Degrees in the upper Ear
diurnal Revolution, is to the Number of Days in
Revolution of the internal Magnet, i. e. as i is to yooc
fo is the refpeffive Motion of this Magnet from  Eaf
Wefi to the real Motion of the upper Earth from V
to Eaft; or to fpeak firialy, fo is the Difference of td
Motions from Weft to Eafi, to the entire Motion of
npper Earth the fame way.   This external fixed E:
has therefore communicated almoff all its Motion alre
to the internal Magnet, and can communicate no nz
than this Difference of their Motion, and that only ii
infinite Term of Years i or, in other Words, this real
ternal Motion can never be the 70oocoth Part fwifter t
it is at prefent. This internal Motion therefore be
f      with the Commencement of the diurnal Motion of
upper Earth ; and has gone on fill fafrer and faflet
the Communication of that Motion thro' the intermed
Fluid. Since therefore Affion and Reaaion are eql
and tend to contrary Parts, this internal Loadflone, t
accelerated by the upper Part, muff have all along
tarded that upper Earth, and made the diurnal Rotai
fill flower and flower. This Acceleration on one Si
and Retardation on the other, muft have been very gi
at the firfi beginning of the diurnal Motion, when
Difference of their Motion was equal to the entire Mot
itfelf; and muft have been diminifhing ever fince.
which Caufe is probably owing that Acceleration of
Moon's Motion with refpedt to that of the Earth, fi.
the time of the old Aftronomers, firfi taken notice of
Dr. Halley, and embraced by Sir I. Newton. And
fanie Confideration feems to fuggeft a Method for det
mining the Age of the World ; for were the Proporti(
of the Quantity of Matter in the upper Earth to the
ternal Magnet, with :the Tenacity of the intermedi
Fluid, Wc. known, one might go back from the kno
Difference of their Velocity now, and find thofe Differ
ces and Quantities of Motion themfelves, a priori, in
pafi Ages ; or were the Velocity of the firf{ diurnal I
tation of the upper Earth known, we might geometrica
determine, a priori, how long ago that Rotation beg
or how antientour Earth is.
XXII. The Variation of Magnetic Needles from i
Azimuth of the Meridians of the internal Magnet ; is 4
rived from the Difference of the Strength of the feve
Parts of the internal Magnet's Surface; which as it is oi
to be known by Experience, that Variation cannot be
termined beforehand, unlefs where there are good
counts how much it had formerly been; it being prol
ble that it returns round, and will be the fame in .
Year of the next Revolution of the internal Magnet, t!
it has been in the like Year of any former Revolution,
will itfelf have a Revolution in about i920 Years.
XXIIL The two fixed Magnetic Poles, in our up]
Earth, firfi introduced by Dr. Halley, as necelfary
folve the Irregularity of the Variation of the Horizon
Needle from the Meridians of the moveable internal ill
net, feem not to have any jufi Foundation in Natur
the like Irregularities being found in the common Terre
or Spherical Loadflones; and being beft accounted
from the Compofition of the Magnets, which are found
have Parts of different Degrees of Purity, Strength, i
Ferfe6tion; fo that where the Parts are weaker than
dinary, the fironger neighbouring Parts prevail, s
draw the Needle that way: not but Dr. Gilbert's Not
of prominent and depreffed Parts on Magnets may hs
fome room, and be allowed to contribute fomewhat
fuch Variations. See Needle.
As to the Caufes of Magnetifin, or the Manner in wh
thefe Phamnomena of the Magnet are produced, we hs
yet no Hypothefis that will fatisfadorily account
them. Plutarcb tells us, the Magnet attraas Iron,
emitting fome fpiritual Effluvia, whereby the contigu
Air being opened and driven on either Side, does ag.
drive that contiguous to it; and thus the Aftion be
communicated round, the Iron is thereby protruded: I
this is contradided by the equally vigorous Affion
the Loadfilone in Vacuo, and in the open Air.  0th
of the Antients afcribe the A61ion of the Magnet
a Soul that animates it;   and others to I know
what Sympathy between the Efiluvia of the Iron a
thofe of the Magnet. The Opinion that principally p
vails among the Moderns is that of Des Cartes, mvv
tained by Malebrancb, Robault, Regis, &c. and even
mitted of and confirmed by Mr. Boyle, &c. In this
fuppofed there is continually flowing, from the Poles
487)                       MAO
~ee&  the World, a fubte, itnpalpable, and invifible Matteei
net, channel'd or firiated 5 which Matter circulating round
be the Earth, in the Plains of the Meridians, re-enter.s* at the
five  Pole oppofite to that from which it if0ued, and paies a-
910  gain thro' the Poles parallel to its Axis: That the Magnet
has two Poles anfwerable to thofe of the Earth, and that
'th's out- of thefe there iffues a Matter like that Jauf men-
the  tioned: That this Matter, entering in at one of the'loles,
coo, gives the Impulfe whereby Iron tends to the Magnet, and
E to  produces what we call Attraffion. Now befides the Mag-
Veft netical Matter re-enteripg the Poles of the Magnet, there
ieir is always a certain Quantity thereof circulating round thd
the  Magnet; compofing a kind of Vortex about it. TheSpace
arth  wherein this Matter moves, is the Sphere of ALivity of
ady  the Magnet, within which its attractive Faculty is con-
1o;0 fined. As to its direffive Faculty, or the Inclination of A
i an  Needle touched with it to the Poles of the World, and its
in- Dip to a Point beneath the Horizon, it follows from the
han  fame Principle; fince were the Magnet or Needle to have
gan  any other Situation, the Magnetic Matter would {trike on
the  its Surface in vain; and not being able to get Admiffion,
by  would, by degrees, change its Situation, till fuch time as
iate its Pores correfponded to the Courfe of the Magnetical
aal, Matter; which Situation having once acquired, it would
hus ceafe to move; the Magnetical Matter then ceafing to
re- diflurb it. The Form of a Magnet therefore is fuppofed
ion  to confiil in its being perforated by an infinite Number of
ide, parallel Pores; fome whereof are difpofed to admit the
,eat firiated Matter from the North Pole of the World, others
the  that of the South; hence the North and South Poles of
-ion  the Magnet.
To     As to the direffive Power of the Magnet, Mr. Wbiflon,
the  from the fl, zd, 3d, &c. Laws of Magnetifm, inclines to
nce  think it mechanical j and afcribes it to magnetic Effluvia
by  circulating continually round the Loadflone; of which
the  Circulation, he thinks, there are evident Indications in
ter- magnetic Experiments; as Mr. Boyle thinks there are of
ons the Magnetifrn or magnetic Effluvia of the Earth ; tho'
in- thofe Effluvia were never yet rendered fenfible as Elec-
iate tric Effluvia begin to be ; but the attraffive Power Mr.
wn   Wbifon thinks entirely immechanical, as the Power of
en- Gravity is; not being able to devife any fuch Motion of
all a fubtle Fluid belonging to the Ltoadflone, as will ac-
Ro- count for the attraffive Power in the fefquiduplicate Pro-
Ily  portion of the Difiances reciprocally ; tho' if he could,
an, yet would that be no more than to remove the immediate
Power of the Supreme Being one Step further; the lafd
the  Refort of all mechanicaljPrinciples whatever being into
de- the immechanical Power Irnd Efficiency of the Deity.
ral    M. Hartfoeker maintains, that the Magnet is no more
nly than a common Stone; full of an infinite Number of
de- hollow Prifms, which, by the diurnal Motion of the
Ac- Earth, are ranged parallel to each other, and nearly pa-
ba- rallel to the Axis of the Earth. Thefe Prifms have their
any  Cavities filled with an extremely fubtle Matter; which,
hat by the diurnal Motion of the Earth, is paffed from
or Prifm to Prifm: thus making a Circulation, and return-
ing into the Prifms where it firsi began: From there
per Principles he deduces all the Phxenomena of the Magnet;
to  and M. Andry does the fame, from the Doctrine of Alkali
tal and Acid.
rag.   There 'are Magnets found in mofi of the Provinces of
e;   China, but the principal Ufe the Chinefe make of them is
llse in Medicine. Le Compte defcribes their manner of cutting
for them by a Machine, which, he fays, is vafily more expe-
to  ditious than any ufed among us.
Lnd    The Magnet is alfo called Lapis Heracleus, from Hera-
or- clea, a City of Magnefia, a Port of the antient Lydia,
Lnd  where it is fuppofed to have been firfi found. Others
ion  derive the word Magnet from a Shepherd of that Name,
ive  who firfl discovered it with the Iron of his Crook on Mount
to  Ida. It is alfo called Lapis Nauticus, by reafon of its Ufe
in Navigation 5 and S&derites, from its attrading Iron,
ich  which the Greeks call 07J'p(9-.
wve    MAGNETICAL AMPLITUDE, an Arch of the Ho-
for rizon, contained between the Sun, at his Riing or Set-
by   ting, and the Eaic and Wefi Point of the Compafs:
ous found by obferving the Sun at his Rifing and Setting by
sin  an Amplitude Compas. See Ampfitude.
ing    MAGNETICAL AZIMUTH. See Azimutb.
but    MAGNETISM, a Term      ufed by fame Chymifts, to
of fignify a certain Virtue, whereby one thing becomes af-
ers fdeced at the fame time with another, either in the fame
to  or a different manner. This is what they otherwife call
not Sympathy.
Lnd    MAGNIFY, a Term chiefly ufed in reference to Mi-
re-  crofcopes, which are faid to magnify Objeffs, or to make
bin- them appearbiggerthan they really are; but, in reali-
ad-  ty, Microfcopesdonot, norcannot, magnify any Qbjea,
'tis  but only fhew it nearer and more of its Parts than before
of were taken notice of. See Microicepe.

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