MAGNETISM. 
110 
MAGTJETISM, /. Any power of attraction.—By the 
'magnetifm of intereft our affeClions are irrefiftibly attracted. 
Glanvi/le's Scepfis .—Power of the load (tone.—Many other 
magnetifns, and the like attractions through all the crea¬ 
tures of nature. Brown .—Phenomena of the magnet, or 
loadftone ; that quality or conftitution of a body or its 
pores, whereby it is rendered magnetical, or a magnet.— 
Magnetifm is found to be a tranfient power, capable of be¬ 
ing produced and deitroyed again. Chambers. 
Of all the phenomena exhibited to us by nature, mag- 
tiftn and eleCtricity may with juftice be confidered as the 
molt extraordinary, fince the caufes of the effeCts produced 
by them have occafioned the greafeft difficulties to philo- 
fophers ; for it muff: be confeffed that, notwithllanding all 
their attempts to explain them, we are as yet acquainted 
only with fads. They have been able indeed to apply 
certain hypothefes to fome of thefe phenomena; but, if 
we examine thefe hypothefes with an unprejudiced eye, 
and without buffering ourfelves to be the dupes of illufion, 
we cannot help acknowledging that they have little foli- 
dity, and that they are fnbjeft to difficulties which cannot 
be removed, as long as we make it a rule to reafon only 
from the known properties of matter,and the laws ofmotion. 
RefpeCting the notions which the ancient philofophers 
entertained about the ca'ufe of magnetic phenomena, we 
know very little. One curious opinion which they enter¬ 
tained of the reafon why a magnet was improved by the 
contaCf of iron, is worth noticing. They conceived that 
the magnet Jed upon the iron, and hence acquired additional 
attractive power; and, when deprived of this pabulum, it 
grew weak and languid : 
-Nam ferro nurunt vitam, ferrique vigore 
Vefcitur; hoc dulces epulas, hoc pabula novit ; 
Hinc proprias renovat vires, hinc fufa per artus 
Afpera fecretum fervant alimenta vigoretn 
Hoc abfente petit, trifti morientia torpent 
Membra fame, venafque fitis confumit apertas. Cldudian. 
The magnetifm of the earth is that property of the ter- 
reftrial globe, from which the magnetifm of the ordinary 
magnets, the direction of the magnetic needle, and other 
phenomena, are derived, and upon which they neceflarily 
depend. This hypothecs is evinced by fo many obferva- 
tions, that no philofopher can be fceptical enough to dif- 
pute its truth. The principal reafons, fays Mr. Cavallo, 
■which prove it, almoft to a demonftration, are, firft, that 
nearly all the phenomena which may be exhibited with a 
common magnet, may be alfo exhibited with the earth, as 
far as it may be tried ; and 1'econdly, that vaft mafles of iron, 
or ferruginous fubftance, aCfually magnetic, are dug out 
of the earth almoft in every part of it. 
Tlie phenomena of the compals and of the dipping-nee¬ 
dle, in different parts of the world, and the magnetifm 
naturally acquired by loft iron when properly fttuated, are 
exaCtly imitated by a common magnet, or a terrella; but 
the only phenomenon which has not been obferved with 
refpeCt to the earth, and which is the principal property 
of the ufual magnets, is the attraction of a piece of iron, or 
other ferruginous fubftance. For inftance, if a piece of 
iron be prefen ted to either of the poles of a common magnet, 
it will be powerfully attracted by it; but, if it beprefented 
to the middle of the magnet, the attraction will be found 
to be hardly perceivable, or at leaft incomparably weaker 
than at the poles ; in conformity to which it might be 
expeCted, that a piece of iron Ihould be attracted more 
powerfully downwards when near the poles of the earth 
than when near the equator; which attraction, being com¬ 
bined with the attraction of gravitation, ought to be known 
by the difference of the weights of .the fame piece of iron, 
when weighed near the poles, and when weighed near the 
equator.; tor, if the magnetic attraction of the earth upon 
it be at all fenfible, it ought to weigh more in the former 
cafe than in the latter. But this difference of weights has 
not yet been afeertained. 
The Laws 0/ Magnetism are laid down by Mr. Whif- 
ton in the following propofitions: 
1. The loadftone has both an attractive and a direCtivs 
power united together ; whereas iron touched by it has 
only the former; i. e. the magnet not only attracts nee¬ 
dles, or filings of fteel, but diretds them to certain dif¬ 
ferent angles, with refpeCt to its own furface and axis ; 
whereas iron, touched with it, does little or nothing more 
than attraCf them ; ftill fuffering them to lie along or 
ftand perpendicular to its furfa%6 and edges in all places; 
without any fuch fpecial direction. 
z. Neither the ftrongeft nor the largeft magnets give a 
better directive touch to the needles than thofe of a lefs 
fize or virtue ; to which it may be added, that whereas- 
there are two qualities in all magnets, an attractive and a 
directive one, neither of them depends on, or is any ar¬ 
gument of, the ftrength of the other. 
3. The attractive powers of magnets, and of iron, will 
greatly increale or diminilh the weight of needles on the 
balance : nay, it will overcome that weight, and fultaia 
other additional weights, too ; while the directive power 
has a much fmaller effeCt. Gaflendus, indeed, as well as 
Marfennus and Dr. Gilbert, maintain, it has none at all ; 
but by miftake ; for Mr. Whilton found, from repeated 
trials on large needles, that after the touch they weighed 
lefs than before. One of 4584^ grains, loft 2§ grains by 
the touch ; and another, of 65726 grains weight, no lei’s- 
than 14 grains. 
4. It is probable, that iron confifts almoft wholly of the 
attractive particles ; and the magnet of the attractive and 
directive together; mixed, probably, with other hetero¬ 
geneous matter; as having never been purged by the fire, 
which iron has ; and hence may arife the reafon why iron, 
after it has been touched, w ill lift up much greater weights 
than the loadftone that touched it. 
5. The quantity and direction of magnetic powers, 
communicated to needles, is not properly, after fuch com¬ 
munications, owing to the magnet which gave the touch, 
but to the goodnels of the fteel that receives it, and to 
the ftrength and pofition of the terreftrial loadftone whole 
influence alone thofe needles are afterwards fubjeCt to, 
and directed by ; fo that all fuch needles, if good, move 
with the fame ftrength, and point to the lame angles, 
what loadftone foever (provided it be good) they have 
been excited by. Nor does the touch ieem to do much 
more in magnetical than attrition does in eleCtrical cafes j 
i. e. it ferves to rub off fome obftruCting particles, that 
adhere to the furface of the fteel, and open the pores of 
the body touched, and fo make room for the entrance and 
exit of fuch effluvia as occalion or affift the powers we 
are fpeaking of. Hence Mr. Whilton takes occafion to 
obferve, that the directive power of the loadftone feems to 
be mechanical, and to be derived from magnetic effluvia 
circulating continually round it. 
6. The abfolute attractive power of different armed 
loadftones is, cateris paribus, according to the quantity, 
not of their diameters or folidities, but of the furfaces of 
the loadftones; or in a duplicate proportion of their di¬ 
ameters. 
7. The power of good magnets unarmed, not fenfibly 
different in ftrength, fimilar in figure and pofition, but 
unequal in magnitude, is fometimes a little greater, lome- 
times a little lei's, than in the proportion of their iimilaj* 
diameters- 
8. The loadftone attracts needles that have been 
touched, and others that have not been touched, with 
equal force at diltances unequal; viz. where the diitances 
are to one another as 5 to 2. 
9. Both poles of a loadftone equally attraft needles, 
till they be, though roughly, touched ; then it is, and 
then only, that one pole begins to attraCt one end, and 
repel the other; though the repelling pole will ftill attraCfc 
upon contaCt, nay, at very imall diltances, notwith- 
Jtanding, 
AO 4 
