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the privilege of resurrection. There are even some aquatic and terrestrial vermiculi more irritable than the eels, since, with the most gentle touch, they contract and swell, until they become many times as thick and short. The objection is therefore confined to this: there are some animalcula which do not revive, though as irritable, even more so than those that do. But it does not affect my hypothesis, for the principle of resurrection is not placed in the greatest and most perfect irritability, but in an irri. tability which, after cessation, may be renewed by means of certain circumstances, though it otherwise appears to be less active than in other animals.

"If this hypothesis does not seem fully applicable to plants, in what concerns their irritability,

since we know only a very small number possessing that property, still it may be applied to what respects their organization. Dried plants in general do not recover life, probably because they are so much injured in drying as to be come incapable of imbibing the juices provided, and converting them into their own substance. Thence do they perish, and are totally destroyed. If such disorder is not occasioned by drying, and the organic action of plants revives when they are softened, and resume their original form, it is undoubted that they will then recover their pristine verdure and natural freshness. This may be the physical cause why the tremella, nostoc, and some other vegetables revive.”

MAGNETISM of the EARTH.

[From Dr. YOUNG'S ANALYSIS of the PRINCIPLES of NATURÁL PHILOSOPHY.]

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earth, and the axis of the magnet coincide with the axis of rota tion.

"Nevertheless, there appear strong objections to this hypothesis-See pinus, p. 300. Ās, 1. Iron is not found to be heavier near the poles, than towards the equator. 2. If a bar of soft iron be held vertical, it is rendered magnetic; if horizontal, it quickly loses that power: therefore in the vertical position it ought to be heavier than in the horizontal, which does not appear to be the caseSee Cavallo, p. 93. 3. If a magnetic needle, lying on a piece of cork,

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cork, be floated on water, it ought always to move to the northern side of the vessel, and not continue at rest in the middle. 4. Though many stones and ores are impregnated with iron, yet they are not in that state magne. tical--Sce Cavallo, p. 16; that is, they will not affect a magnetic needle, though they themselves may be affected by a magnet. 5. The magnetism of the earth seems incompatible with the variation of

the needle.

"62. The poles of any magnet will be directed one towards one of the magnetical poles of the earth, the other towards the other.

"This follows from art. 7 and 61. The pole which is directed towards the north pole of the world, is called the north pole of the magnet; the other the south pole.

"63. The magnetic axis of the earth is not coincident with the

axis of revolution.

"For the north pole of the magnet is not directed exactly towards the pole of the world. This is called the variation.

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64. The magnetic needle is subject to a diurnal variation, moving in northern latitudes, generally towards the west before noon, and afterwards gradually returning. "It has been conjectured that "It has been conjectured that this may arise from the diurnal change in the heat of the earth; for the eastern parts of the earth being heated faster in the morning than the western, their attractive force on the needle will be weakened, by art. 18, and therefore the needle will move westward.

"But the magnetical nucleus, to which we attribute the direction of the magnetic needle, is

certainly buried at a very conside rable depth below the surface of the earth; whereas we know that the line which separates the terrestrial crust, subject to the influence of heat and cold, from that which is not subject to it, does not lie far below the surface; for in caves of even moderate depth, the thermometer preserves a permanent state.

"65. The magnetic needle is subject to an annual variation.

"Dr. Halley endeavoured to account for this phenomenon, by supposing that the axis of the magnetic nucleus was not exactly coincident with the axis of the earth, and that this nucleus was also moveable within the body of the earth. However, it has been found that the variation is not regular in any place, as it ought to be on this hypothesis. It is however singular, that the atites, or eagle stone, which is of the class

which is frequently moveable in the

of iron ores, contains a nucleus,

centre of the stone. See Fourcroy's Chem. v. iii. p. 219.

"66. The aurora borealis produces irregularities in the declination of the needle.

alis the needle is, in general, much "For during an aurora boredisturbed, while a similar needle of brass is not at all agitated. Since it is unquestionable that the au rora borealis has a magnetical influence on the needle, and that the needle is subject to a daily varia exists daily in the atmosphere, so as tion, perhaps the aurora borealis to produce this daily variation, and

the annual variation also.

"67. If a magnet be sus pended on an horizontal axis at its centre of gravity, so that it may vibrate in a vertical circle, the north

pole

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 predominant. 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 mag netic, 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 immediately 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 perhaps 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

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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. Íf the horizontal bar be rubbed both ways, from the middle to the two extremities, it will have two south poles, one at each end, and a north 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 pola rity 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 produced by the strokes of the hammer at each end of the bar. If it be reversed, by parity of 03

reason

reason we infer, that the greater part of the particles have the position of their poles inverted.

"76. The electric shock frequently gives polarity to iron bars through which it is transmitted.

"For in its passage through the bar it agitates the particles of the iron, and therefore produces an effect 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 principle of exciting a tremu fous 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 magne tic 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 MAGNETISM.

"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 put 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 magnet on the filings, each particle becoming itself a magnet; so that there are formed several strings of magnets, reaching from one pole of the central and principal magnet to the other.

that the existence of a magnetic "79. Nevertheless, it seems 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 which their action and force may any thing else, by and through be conveyed from one to another, is to me so great an absurdity, that I believe no man, who has tent faculty of thinking, can ever in philosophical matters a compefall into it.' ley's Newton, vol. iv. p. 438. See bishop Horse

"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 phenomena, 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.

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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, The whole of

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substance may any 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, and the remote end of it the same kind of electricity; so in magnetism, and in this case, the neutral point is analogous to the magnetic centre, 5. The different kinds of electricity and magnetism sometimes succeed each other 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 bodies. 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 magnets.

"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

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