MA'GNETIS M. 
.pole, between A B and D C, it appears to go nearly fl raight 
on ; towards the Tides it proceeds in lines more and more 
curved, till at lad the curve lines from both poles exaftly 
meeting and coinciding form numberlefs curves on each fide, 
nearly of a circular figure, as reprefented in the diagram. 
A fmall artificial magnet may be ufed in this experi¬ 
ment inftead of the real magnet, with a fimilar effeft. If 
the table on which the paper refts receives a few gentle 
knocks, fo as to (hake the filings a little, they will the 
more readily difpofe theinfelves round the magnetic bar ; 
otherwife, the aftion of the magnet will not have power 
fufficient to difpofe properly thole particles which lie at a 
confiderable diftance. This phenomenon, which has been 
obferved from time immemorial, has led various perfons 
to believe, that a certain fluid circulates from one of the 
poles of every magnet to the other, in confequence of 
which the iron or fteel filings are thus arranged round the 
magnet. A little confederation will evince the abfurdity 
of this fuppofed circulation ; becaufe, if the fluid, of what¬ 
ever nature it may be, did really circulate from one pole 
to the other, and had any aftion on the filings, thefe would 
be all driven toward that pole to which the moving fluid 
direfted its courfe. The true caufe of the arrangement 
of the filings is, their becoming actually magnetic, and 
their two extremities being pofleffed of different polarities. 
Suppofe, firlt, that only one oblong particle of iron be 
affixed to the various parts of the furface of the magnet, 
it is evident, from what has been already faid, that on the 
poles this particle of iron, A B, fig. 3, would Hand per¬ 
pendicular to the furface, becaufe its farther extremity B, 
having the fame polarity as the extremity C of the magnet, 
is equally repelled by it on every fide, and is far from the 
influence of the other extremity D; on the Tides near to 
the poles the faid particle will hand inclined, becaufe the 
fartheft pole of the magnet begins now to aft upon it ; 
and on the middle of the magnet the wire will lie quite 
ciofe to it, or, if it be kept at fome diftance, will lie pa¬ 
rallel to the magnet, becaufe the two poles of the magnet, 
being equidiftant from the extremities of the iron parti¬ 
cle, have an equal aftion upon it. Now, when there are 
many particles of iron, viz. the filings, near the magnet, 
Ihofe particles which touch its furface are rendered mag¬ 
netic, confequently they attract other particles ; and thefe, 
being made alfo magnetic, attraft others, and fo on ; form¬ 
ing firings of fmall magnets, which gradually decreafe in 
power as they recede from the magnet. As each of thefe 
particles has two magnetic poles, by a little confideration 
it will appear, that the fartheft ends of thofe firings or 
lines which proceed from the parts adjacent to one of the 
poles of the magnet, for inftance, the north, are likewife 
pofleffed of the north polarity, and the fartheft extremi¬ 
ties of thofe firings which proceed from the pacts adjacent 
to the fouth pole of the magnet, are pofleffed of the fouth 
polarity ; hence, when they come fufficiently near, they 
attraft the extremities of the former firings, and confe¬ 
quently form the curves delineated on the figure. 
Another familiar method of fnowing the aftion of the 
poles of a magnet, is the following: Take two femicir- 
cular magnets, and dip their extremities into iron-filings. 
The filings will of courfe adhere to the extremities of the 
magnets, and will appear as if radiating from them. Now, 
prefent the two magnets with their adhering filings to 
each other, fo that the north and fouth pole of the one 
is oppofite to the contrary poles of the other, and the iron- 
filings at their extremities will approach each other, and 
coalefce, as reprefented at fig. 4. But, if you prefent them 
to each other fo that their correfponding poles may be 
mutually oppofed, the filings at their extremities will dart 
back, and leave a vacancy between the oppofed poles of 
the magnets, fomevvhat like what is reprefented at fig. 5. 
When a common magnet that is freely l'ufpended, has 
only two poles, it will place itfelf very readily in the mag¬ 
netic meridian, or in that place in which other good mag¬ 
nets are wont to place themfelves; but, when it has more 
than two poles, it may happen that thefe poles are fo fitu- 
Vol.XIV. No. 960. 
1J3 
ated, as that the magnet will not traverfe; that is, it will 
have no direftive power, and yet it will attraft, repel, See, 
Ifwo circumftances deferve to be noticed with refpeft to 
magnets that have more than tw o poles. One is, that the 
parts adjacent to one pole are pofleffed of a contrary po¬ 
larity ; and the other is, that the number of poles of one 
denomination in a magnet is either equal to, or differs 
from, the number of poles of the other denomination l>v 
one; thus, if the magnet has four fouth poles, then it will 
have either four, three, or five, north poies. It is obferved, 
that good magnets of an uniform texture and proper form 
have only t wo poles, an-d they lie in oppofite parts of their 
furfaces, fo that a line drawn from the one to the other 
paffes through the centre of the magnet. The polarity of 
a magnet, however, mull not be underfiood to refi'de only 
in two points of it; for, iu reality, it is the half, or a 
great part, of the magnet that is poffefled of one polarity, 
i. e. has the property of repelling the contrary pole of 
another magnet; and the re it of the magnet is pofleffed 
of the other polarity ; the poles being, "therefore, thofe 
points in which that power is the ftrongeff. 
If two magnets be fphericnl, one will turn or conform 
itfelf to the other, fo as either of them would do to the 
earth; and, after they have fo conformed or turned them¬ 
felves, they will endeavour to approach or join each other; 
but, if placed in a contrary poiition, they will avoid each 
other. This property may be illuftrated by placing two 
magnets on fmall pieces of wood, formed in the fhape of 
boats,and fwimmingfreely on flagnated water, undifturbed 
by wind, and at fuch a diftance as to be within the fphere 
of each other’s aftivity ; both the boats will fwim towards 
each other with an accelerated motion, and meet exactly 
in the middle of the diftance between them, provided that 
the boats and magnets were exaftly of the fame weight 
and bulk ; but if either boat be turned, fo that its mag¬ 
net may prefent a contrary end to that by which it was 
attracted by the other magnet, they will both recede from 
each other with an equal velocity. The fame phenome¬ 
non may likewife beCxhibited by fufpending a magnet, C, 
from the end B of a balance, fig. 6. and, forming an equi¬ 
librium with a weight in the fcale A, place another mag¬ 
net, D, under C, and C will be found to rufh towards D, 
and to lift the weight in the fcale A ; but, if the oppofite 
end of D be prefented to C, C will be repelled by it, 
afcend, and the fcale A will defeend ; if D be placed 
above C, as in E, the eftefts will be juft the contrary. 
M. Mulchenbroeck found by a variety of experiments, 
that two magnets attraft one another with different forces 
at different diftances ; that they aft moft ftrongiy in mu¬ 
tual contaft, in which cafe their force has been equal to 
the weight of 340 grains, bur at the diftance of twelve 
inches equal only to 23 grains; nevertheless, they ob- 
ferve no regular proportion in their decreafe, but the ratio 
is lefs than the inverfe of their diftances; and different in 
different magnets and at different times. There are fome 
whbfe fphere of aftivity reaches even to fourteen feet, and 
others in which it is not fenlible at the diftance of eight 
or nine inches. He has alfo found, that the fphere of re- 
pulfion varies in different magnets, and at different dif¬ 
tances; and that the repulfive force is much lefs than that 
of attraftion; the latter in contaft being equal to 340 
grains, whereas the former is equal only to 44 grains. It 
appears alfo from another experiment of the fame author, 
that the repelling forces of both poles of the fame magnet 
are very confiderable at the diftance of twelve lines, beino- 
equal to 30 grains, that they increafe to the diftance only 
of feven lines, where they are equal to 36 ; nut that 
in immediate contaft they are equal only to 13 grains. 
Mr. Michel], however, differs much in his deductions from 
thofe above-mentioned ; he maintains, that each pole afts, 
attrafts, or repels, exaftly equally, at equal diftances, in 
every direction ; and that the rnagneticai attraftion and 
repulfion are exactly equal to each other. He adds, that 
the miftake of thofe who think otherwife, arofe from theic 
not attending to the different degrees of ftrength which 
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