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pole of the magnet, on the northern side of the equator, will be depressed; and the southern pole
depressed in the southern latitudes. .
“Because, in northern latitudes the influence of the northern magnetic pole of the earth is predominam. This is called the dipping needle. At the equator there is no dip. If a needle were placed exactly E. and W. at the equator, it would remain so ; but on the slightest agitation it would traverse, and point N. and S.
“ 68. If a bar of soft iron be kept vertical, or rather parallel to the magnetic axis of the earth for some time, it will become magnetic, the lower end acquiring a north polarity in the northern latitudes; but in the southern parts of the earth it acquires a south polarity. On reversing the bar, the poles are imo changed. This follows from art. 33 and 61.
“ 69. In northern latitudes, the south pole of a magnet is stronger than the north pole.
“ 70. If an iron bar made red hot, be left to cool in the magnetic line, it will acquire a degree of magnetism, which is more or less permanent according to the nature of the iron.
“ For the iron, while red hot, is soft, and therefore the earth, or o: some atmospherical cause, can more easily render it magnetical; but when cooled, it becomes harder, and consequently more tenacious of the power it has acquired.
“ 71. If an iron bar held vertical be rubbed always in the same direction against an horizontal bar from one end to the other, the horizontal bar will become mag
netical, that extremity which was first touched, being the north pole in the northern parts of the earth, “For the vertical bar either by the action of the earth, or of some cause existing in the atmosphere, becomes a magnet, whose lower end therefore acquires a north polarity by art. 68 ; therefore, by art. 48. the extremity last touched acquires a contrary polarity, that is, a southern polarity; and of course the extremity which is first touched, acquires a northern polarity. “ 72. If an horizontal bar be rubbed from both ends to the middle, it will have two north poles, one at each end, and a south pole in the middle. “ 73. If the horizontal bar be rubbed both ways, from the middle to the two extremities, it will have two south poles, one at each o and a # pole in the middle. “ 74. If an iron bar be held vertical, a few smart strokes of a hammer will give it polarity. “This shows that a certain disposition of the particles of iron is requisite, in order that it should be magnetical ; which is the opinion of Van Swinden. See his Memoirs, vol. i. p. 479.
“.75. If a bar, weakly magnetised, be held vertical, and struck alternately at each end, its polarity may be destroyed or reversed. “If the polarity be destroyed, we may conclude, from art. 38, that the homogeneous poles of the component or elementary magnets are thrown into contrary positions, by the contrary vibrations roduced by the strokes of the #. at each end of the bar. If it be reversed, by parity of () 3 reason
The electric shock fregives polarity to iron rough which it is trans
“ 76. quentl bars mitted. “For in its passage through the bar it agitates the particles of the iron, and therefore produces an efiect similar to that in art. 74. So that electricity, as such, does not contribute to the communication or destruction of the magnetic virtue, but merely on the Fol. of exciting a tremuous motion amongst its particles, so as that the earth or atmosphere may give that disposition, on which polarity seems to depend. “77. The aurora borealis is probably a magnetic meteor. “ For, 1. the northern pole of the needle appears to follow the aurora borealis—See Van Swinden's Mem. vol. i. p. 247. 2. The rays of the aurora borealis seem to converge to the magnetic pole. See Mairan, and Encyclop. Brit. also Cavallo, p. 331, and Meteorological Observations and Essays by J. Dalton, an. 1793. 3. A magnetic needle appears much disturbed during an aurora borealis, while a similar needle of brass is not agitated.”
of The cause of MAGNET is M.
“ 78. There is no direct experiment by which the existence of a magnetic fluid can be proved.
“ The opinion that magnetism was occasioned by a fluid, entering in at one pole, and passing out at the other, took its rise from
the following experiment: having ut a small magnet among some iron filings, laid upon a piece of paper, give the table a few gentle knocks with your hand, so as to shake the filings a little, and they will dispose themselves in curves terminating at the poles, and concave towards the axis of the magnet. But this effect is occasioned merely by the action of the mag- . net on the filings, each particle becoming itself a magnet; so that there are formed several strings of magnets, reaching from one pele of the central and principal magmet to the other."
. “ 79. Nevertheless, it seems that the existence of a magnetic fluid must be admitted; because we cannot conceive a body to act where it is not. “‘That gravity,” says sir Isaac Newton, “should be innate, inherent, and essential to matter, so that one body may act, upon another at a distance, through a va." cuum, without the mediation of any thing else, by and through which their action and force may be conveyed from one to another, is to me so great an absurdity, that I believe no man, who has in philosophical matters a competent faculty of thinking, can ever fall into it.’ See bishop Horseley's Newton, vol. iv. p. 438.
“80. It seems probable that magnetic phenomena arise from causes existing in the atmosphere.
“The magnetic needle is certainly affected by atmospherical causes; and therefore all its phemomena, perhaps, depend on the same causes. The magnetism of the earth is an hypothesis, but the influence of atmospherical causes
on the needle is a fact. “ St.
“ 83. The causes of electricity and magnetism are different. “ Because, 1. Electricity acts on all bodies, magnetism on iron only. 2. Electricity affects the senses, magnetism does not. 3. points neither supply nor absorb the magnetic fluid more abundantly than blunt bodies, as they do in electricity. 4. Moisture diminishes electrical action, but has no influence on magnetism. 5. *The whole of any substance may acquire one kind of electricity throughout ; but every magnetic body has both kinds of magnetism. 6. The aurora borealis is not an electrical meteor, yet it influences the magnetic needle.
“ 84. Though the electric and magnetic powers are different, yet there subsists a strong analogy between them. )
“As, 1. Electricity is of two kinds; so is magnetism." 2. Bodies similarly electrified, or similarly magnetised, repel each other; if dissimilarly, they attract each other. 3. There is no electrical or magnetical attraction except between bodies differently electrified or magnetised. 4. If a body be brought near another
which is electrified, its end next the electrified body acquires the contrary electricity, . the remote end of it the same kind of electricity; so in magnetism, an in this case, the neutral point is analogous to the magnetic centre, 5. The different kinds of electricity and magnetism sometimes succeed each . alternately, for several times, in the same body; so also in magnetism. 6. One kind of electricity or magnetism cannot be produced without the other. 7. A body more powerfully electrified or magnetised than another which is in the contrary state, when applied to it, will change its electricity or magnetism. 8. If an excited electric be broke transversely, the parts which were before in contact will be found diversely electrified; so in magnetism. 9. The electric and magnetic powers are proportional to the surfaces, not to the solid contents of the electrified and magnetic iodies. 10. A considerable degree of heat destroys both electricity and magnetism.
“ 85. Animal magnetism appears to be a mere figment; and all the effects ascribed to it have been produced either by the imagination, or by drugs secretly applied.
“ 86. Medical effects have been produced on the human body by ...the external application of maglmets.
“. It appears that the magnet acts as a sedative or antispasmodic. Brimstone and camphor, applied externally to the body, have been found to act in the same manner. Hence we may derive another argument in favour of
- 0 + the the existence of a magnetic fluid ; for we can scarcely suppose that the magnet produces this effect by its merely attracting or repelling the particles of iron which are in the blood. But this seems to be put beyond all doubt by
observing, that the magnet does not act upon the particles of blood until they have been calcined; and therefore can have no influence on the animal body mere. ly by its attractive power.”
HEN, at the Despot's dread command,
Not so the British muse—Tho' rude
Her voice, to Graecia’s tuneful choir, By dread, by danger unsubdu'd,
Dauntless she wakes the lyric wire: So when the awful thunder roars, When round the livid lightnings play, The imperial eagle proudly scars, And wings aloft her daring way.