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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 486


MAG
(.486')
MAA O
he takres otcafion to obferve,
of the Loadftone feemas to b
derived from magnetic Efflus
sound it.
VI. The abfolute attractive
Loadilones, is, ceteris paribms,
rot of their Diameters or Soli
of the Loadfilones; or in a Di
Diameters.
VII. The Power of good m
bly different in Strength, fimi
but unequal in Magnitude, is
Sometimes a little lefs than ih
fimilar Diameters.
>VIII. The Loadflone attra&
touched, and others that hav
equal Force, at Diflances une
flances are to one another as 5
IX. Both Poles of a Loadilor
till they be, tho' roughly, touw
only, that that one Pole begin
repel the other: tho' the rei
tra&S upon Conta&i, nay at ver
flanding.
X. The attraffive Power oi
milar Pofition to, but different
Needles, is in the Sefquidupli
filances of their Surfaces from t
or as the mean Proportionals
the Cubes of thofe Diflances rec
Roots of the fifth Powers of tI
Thus the Magnetic Power of
Diflance from the Surface of th
fifth and fixth Part of that Po
At thrice the Diflance the Po
and i6th Part, at four times t
32 times as fmall, and at fix ti
as fmall. Where it is to be
are not taken, as in the Law c
ter; but the Surface: all Ex
the Magnetic Power refides
the Surfaces of Loadf{ones and
cular Relation to any Center
here laid down was determine(
great Number of Experiments
Taylor, and bimfelf. The Fon
Chords of thofe Arcs, by whi
Diflances, draws the Needle oi
to which Chords (as he has dei
portional. The Numbers in fc
Trials he gives us in the follo'
half the Chords, or the Sine
Declination, as the true Meafu
netifm.
Di/fance in  Degrees of
Incbes.    Inclination.
20           2
14            4
13 T--       6
12    --
I I  *--      10-'
I04 -I2
9 -T
Xl. An Inclinatory, or Dippi
Radius, and of a Prifmatic or (
ofcillates along the Magnetic I
every mean Vibration in about
fmall Ofcillation in about 5 " I
kind of Needle, four Foot long
cillation in about 24 z", and e
22 i.
XII. The entire Power of M
as it effects Needles a Foot lot
nearlyas i to 300; and as it a
long, as x to 6oo.
XIII. The Quantity of Maf
the fame Dipping-Needle, as
vertical Planes, is everas the Cc
by thofe Planes, and the Magnt
Horizon.
Coroll. Thus if we would eflit
ces in the horizontal and vertics
London ; we fhall find that the
long, is, to the entire Force aloi
as 96 to ioo; and in Needles fi
lCooo: whereas in the former,
dies a Foot long, is as a8 to I00
that the direAive Power  long, as 256o to 0oooo.  Whence it follows, that
the
e mechanical; and to be Power by which horizontal Needles are governed inthefe
via, circulating continually  Parts of the World, is but one quarter of the
Power by
which the Dipping-Needle is moved.
Power of different armed   Hence alfo, fince the horizontal Needle is moved
on-
according to the Quantity, ly by a Part of the Power which moves the Dipping-Nee-
dities, but of the Surfaces die ;  and that it only points to a certain Place
in the Ho-
uplicate Proportion of their rizon, becaufe that Place is the neareft its
original Ten -
dency, of any, its Situation will allow it to tend to: When
'agnets unarmed, not fenfi- ever the Dipping-Needle flands exaaly perpendicular
to
lar in Figure and Pofition, the Horizon, the horizontal Needle will not refpe&t
one
Sometimes a little greater, Point of the Compafs more than another, but will
wheel
i the Proportion of their about every way uncertainly.
XIV. The Times of Ofcillation and Vibration, both
s Needles that have been  in dipping and horizontal Needles equally good,
is as
'e not been touched with  that of their Lengths direclly; and the aftual
Velocity of
qual, viz. where the Di- their Points along their Arcs always equal.
to 2.                      Hence Magnetic Needles are, cxteris paribus, fill
bet-
ie equally attraa Needles,  ter the longer they are; and that in the fame
Proportion
ched ; then it is, and then  with their Lengths. See Needle.
s to attraa one End, and   XV. The Earth, on which we live, includes within
it
telling Pole will fail at- a vaft Spherical Magnet, concentrical thereto,
with its own
y fmall Diflances notwith-  Poles, Meridians, Equator, and Parallels; and
all much
of the fame general Nature with thofe of fmall Terrelle,
f Loadflones, in their fi- or Spherical Loadflones, in the poffeffion of
the Curious
Difiances from Magnetic  among us.
cate Proportion of the Di-  XVI. The Power of a good Terrella, or Spherical
Load-
hofe Needles reciprocally; flone, as it affeds a Needle a Foot long, is equal
to the
between the Squares and  Magnetic Power of that internal Loadflone about
two and.
:iprocally; or as the Square  an half, or three Diameters off fuch Loadflone.
From
iofe Ditlances reciprocally.  which Confideration the Q uantity of Magnetic
Attraftion,
Attraffion, at twice the  at all Diflances from the internal Loadftone, for
Needles
eLoadilone, is between a  a Foot long, may be determined; and from  the fame
ewer at the firl Diflance. Confideration it appears, that the Diameter of
ithis inter-
wer is between the I5th  nal Loadflone is about I1 50 Miles.  To which we
ma
the Diflance the Power, is add, that, in regard Sir Ifaac Newton has demonfirated
imes the Diffance88 times that the Power of Gravity diminishes within the
Earth$
noted, that the Diflances  and is letler there than at its Surface nearly,
in the pro-
)f Gravity, from the Cen- portion of its greater Nearnefs to the Center;
the Magne-
perience affuring us, that tic Power at 2900 Miles diflance from us, and
nearly io6o
chiefly, if not wholly, in from the Earth's Center, which is 24f of the Power
of
Iron ; without any parti- Gravity here, will be fomewbat greater than the
Power
at all.  The Proportion  of Gravity there: Which Limit is worth our Attention,
I by Mr. Whifon, from  a  Gravity being flronger than Magnetifin on the one
Side
of Mr. Hauksbee, Dr. Brook, of it, and weaker on the other; we mean as it
affeds
ce they meafured by the  Needles of one foot Diameter. At that Limit, there-
ich the Magnet, at feveral fore, at leafl near the Magnetic Poles, Iron,
a Foot long,
at of its natural Direafion, will be twice as heavy, and fall twice as fafl
as any other
monffrated) it is ever pro- natural Body, viz. by the Union of thofe two
equal
ime of their moll accurate  Powers, Gravity and Magnetifin; and of consequence,
a-
wing Table, fetting down  bove that Limit, fuch an Iron will be lefs than
twice as
s of half thofe Arches of heavy; below it, more than twice as heavy as any
other
res of the Power of Mag- natural Body.
XVII. The Earth's internal Loadfilone is not fixed to
our upper Parts, but is moveable with refpect thereto,
Sines of  Ra't.and a Eually revolves on the Earth's Axis from Eajt to
Snesof.     Radt Sefqui-  Wefi in a certain long Period of Time ; as appears,
be-
Arcs.     du'pl.     yond Contradilion, from the conflant Variation of the
horizontal Needle Wefiward; as well as the regular In-
-I75-            466     creafe of Inclination of the Dipping-Needle.
-349       -         z16   The only way to render this Motion, i. e. the
Variation,
--523       --       70  poffible and intelligible (to ufe Dr. Halley's Words)
is
697    -   -138       to fuppofe it to turn about the Center of the Globe
-871             105     having its Center of Gravity fixed and immoveable
in
- 1045--     -      87   the fame common Center of the Earth. This moveable
- 1219   '       70      internal Surface muff likewife be loofe, and detached
from the external Parts of the Globe ; which may bo
ing-Needle, of fix Inches reckoned the Shell, and the other the Nucleus,
or inner
Cylindric Figure, when it Globe, included within it, with a fluid Medium
between.
Meridian, performs, here, Now from the Variations moving Weilwards, 'tis
plain,
6 " or 360 h'J; and every  that the forefaid Nucleus has not precifely
attained the
or 33o All; and the fame  fame Degree of Velocity with the exterior Parts
in their
g, makes every mean Of- diurnal Revolution ; but fo nearly equals it, that
in 365
-very fmnall one in about Revolves 'the Difference is fcarce fenfible ; and
mufl
probably have arifen from  hence, that the Impulfe,
agnetifm in this Country, whereby the diurnal Motion was impreffed on the
Earth,
1g, is to that of Gravity  was given to the external Parts, and thence communi-
iffefs Needles four Foot cated to the internal.
XVIII. This internalMa ~net has one central Pole North-
gnetic Power accelerating  wards, in the nature of he Poles of our common
Load-
it oscillates in different flones; but its Southern Pole appears not to be
central, but
)-fines of the Angles made  rather circular; and that at a great Diflance
from  the
,tic Meridian taken on the  Southern Pole of the Earth.
XIX. The Northern Magnetic Pole is now fituate a-
nate the Quantity of For- bout the Latitude of 76 Deg. ,, 4. e. 13 Deg. !
from .the
Ll Situations of Needles at North Pole of the Earth, and about 30 Deg. Eaflward
latter, in Needles a Foot from the Meridian of London.
ig the Magnetic Meridian,  XX. The Southern Magnetic circular Pole has its
fur Foot long, as 9667 to  Center, or central Pole, nearly in the Parallel
of 6o De-
the entire Force in Nee- grees; and in a Meridian pafirng along the Eaft
Coaff of
; and in thofe four Foot Borneo, about I1 7 Degrees Eaftward of London: its
Ra-
dius
i'


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