MAGNETISM. 
112 
much it had formerly been ; it being probable that it-re- 
turns round, and will be the fame in any year of the next 
revolution of the internal magnet that it has been in the 
like year of any former revolution ; or will itlelf have a 
revolution in about 1920 years. 
23. The two fixed magnetic poles in our upper earth, 
fir It introduced by Dr. Halley, as neceffary to folve the 
irregularity of the variation of the horizontal needle from 
the meridians of the moveable internal magnet, feem not 
to have any juft foundation in nature, the like irregula¬ 
rities being found in the common terrellae, or fpherical 
loadftones, and being belt accounted for from the compo- 
fition of the magnets, which are found to have parts of 
different degrees of purity, ftrength, and perfection ; fo 
that, where the parts are weaker than ordinary, the ft ranger 
neighbouring parts prevail, and draw the needle that way ; 
not but Dr. Gilbert’s notion of prominent and depreffed 
parts on magnets may be allowed to contribute f'omevvhat 
to fuch variations. 
Thus far Mr. Whifton ; to fome of whofe laws, as here 
laid down, objections have been made ; and fome difeo- 
veries have been made fince his time, which we fiiall have 
•Occafion to notice as we proceed. 
PROPERTIES of NATURAL MAGNETS. 
If the mineral body called magnet orloadfione be brought 
within a moderate diftance from a piece of iron or fteel, 
or other ferruginous body, fuch as a fmall key, a fewing- 
needle, or the like, the ferruginous body will approach 
the magnet; and, if no obftacle intervene, will come in 
contaft with it, and the two bodies will adhere together, 
fo as to require an evident force to feparate them from 
each other. 
Again, if a magnet be freely balanced, fo that it be left 
at liberty to affume any direction, as if it be fufpended by 
a thread, or made to float on the furface of water by placing 
it on a piece of cork or wood, it will foon fettle itfelf in 
one particular direction, fo as to turn one part of its fur- 
face towards the northern point of the horizon, and the 
oppofite part of courfe towards the fouthern point. 
Thefe two parts of the furface of the magnet are called its 
north and Jouth poles ; this property of the magnet, of af- 
furning this particular direction, is called its polarity, or 
its diredive power ; and, when a magnet is placed fo as to 
arrange itfelf in fuch a direction, it is faid to traverfe. 
The direction in which a fufpended magnet finally fet¬ 
tles is called the magnetic meridian ; and it is different in 
different places, and at different times. It is generally, 
however, very different fix..' the real meridian line, fo 
that the north pole of a magnet declines a lbtle to the 
ealt or weft, and the fouth pole to the welt or eaft. The 
difference of the magnetic from the altronomical meridian, 
is called the declination or variation of the magnet; and the 
declination is faid to be ealt or weft, according as the 
north pole of the magnet verges to the one or the other of 
thefe points. 
If an oblong magnet be fufpended on a pivot by its 
centre of gravity, it does not fettle in a perfectly horizon¬ 
tal pofition, but one of its poles is depreffed below the 
horizontal line, and the other elevated as far above it, 
'making an angle with the horizon that is alfo different on 
different parts of the earth’s furface. This deprefiion of 
one of the poles is called the dipping of the magnet. See 
Compass, vol. iv. and Dipping-needle, vol. v. 
It two magnets that are each freely fufpended, be brought 
within a moderate diftance from each other, fo that the 
north pole of the one is oppofed to the fouth pole of the 
other, they will attraCI each other; and, if no obftacle in¬ 
tervene, will rufli together; but, if the two north poles 
or the two fouth poles be mutually oppofed, the magnets 
will repel each other. 
Such are the leading properties of what is called the na¬ 
tural magnet ; but what is of more importance, as we (hall 
•fee hereafter, any piece, of iron or fteel may, by being 
rubbed with a natural magnet, or by fome other procefles 
to be afterwards explained, be made to acquire the fame' 
properties, and thus in every ufeful refpeCt l'erve the fame 
purpofes as the natural magnet. Thefe pieces of iron or 
fteel thus magnetifed, are called artificial magnets ; and, 
when they are of a (lender oblong form, they are termed 
magnetic needles. When we fpeak of the polarity, the de¬ 
clination, or the dipping, of the magnetic needle, we would 
be underftood as alluding to thefe (lender, oblong, artifi¬ 
cial needles. 
A ftraight line joining the two poles of a magnet is 
called its axis, and a line drawn tranfverfely on the fur¬ 
face of the magnet, perpendicular to the axis, is called the 
equator. 
The properties of natural and artificial magnets above 
enumerated, are attributed to the agency of fome unknown 
force or power, either inherent in the magnet, or imparted 
to it by the procefles to which it is fubjeC'ted. This force is 
called magnetifm, or the magnetic power, reftriCting the terra 
magnetifm to the fcience that illuitrates and attempts to ex¬ 
plain the phenomena. 
The mod; important property of the magnet is its po¬ 
larity, as it is by means of this that the mariner is ena¬ 
bled to find his way along the tracklefs ocean, where, be¬ 
fore the difeovery of this important property, he had no 
other guide but the (tars, and could therefore feldom ven¬ 
ture far from the coaft; as to which, fee the article Com¬ 
pass, vol. iv. It is by this property too, that the miner 
is enabled to purfuea direCt courfe through the bowels of 
the earth, or the traveller direCt his fteps through immenfe 
forefts, or over Tandy deferts. The ufes of the magnet are 
therefore obvious and important, and the fcience which 
places thefe ufes in the beff point of view; and thus ena¬ 
bles us to turn them to the greateft advantage, is well de- 
ferving our attention. Many of the faCts to be related 
under this article are highly curious, and form a pleafing 
addition to thofe fcientific amufements which are fo well 
calculated to excite the attention of beginners in the ftudy 
of experimental philofophy. 
Sir George Staunton, in his Account of the Embaffy 
to China, has given a curious figure of the Chinefe Nep¬ 
tune, who has a temple at Ta-coo, where he is worfhipped 
under the appellation of Toong-hai-vaung, or king of the 
Eaftern Sea. The reprefentation is emblematic^ of the 
element over which he is confidered as prefiding. He (its 
upon the waves with firmnefs, eafe, and dignity; and, 
though he brandifties no trident, “ to call up monfters 
from the vafty deep,” yet he feems to be confcious of fe- 
curity by the poffellion of a magnet in one hand, while the 
dolphin, which he holds in the other, denotes his power 
over the inhabitants of the ocean. His beard flowing in 
all directions, and his agitated locks, feem intended for 
a perfonification of that troubled element. The circum- 
ftance of thedivinity’s reliance upon a magnet, isa fufticient 
indication how intimately the knowledge of its properties 
has been incorporated with the mythological doctrines of 
the Chinefe; as well as at what an early period that know¬ 
ledge muft have been applied to navigation. They who 
fuppofe, indeed, from variousallulions in ancient authors, 
as well as from a confideration of the facility with which 
pieces of iron placed in-particular pofitions acquire mag¬ 
netic qualities, that thefe were known in Europe alfo in 
very remote ages, conjecture that the trident.itfelf in the 
hand of Neptune is leis a magic wand, than an emblem of 
that unerring guidance which the magnet is capable of 
fupplying. We thought this reprefentation fo curious, 
that we have copied it in the centre of the annexed Plate, 
as a frontifpiece to this article. 
The direction of the (luppofed) magnetic effluvia, in 
palling out of the (lone,, may be exhibited to the fight in 
the following manner. Let AB, CD, fig. 2. be the poles 
of the magnet; about every fide gently ltrew fome iron 
or fteel filings on a (beet of white paper ; thefe fmall par¬ 
ticles will be affeCted by the effluvia of the Itone, and fo 
difpofed as to (how the courfe and direction of the mag¬ 
netic particles in every part. Thus, in the middle of each 
pole. 
