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Justead, therefore, of the glass-cylinder, con ductor, coated jar, &c., used in electrical experiments, the Galvanic pile, or trough, is now preferred

Obs. The common exhibition of electrical effects, is in attractions and repulsions, in which masses of matter are concerned; but there are other effects, in which, the changes that take place, operate, in a manner, in small spaces of time imperceptibly; and in which, the effects are produced upon the chemical arrangements of bodies.

If a piece of zinc and a piece of copper be brought in contact with each other, they will form a weak electrical combination, of which, the zinc will be positive, the copper, negative this may be learnt by the use of a delicate condensing electrometer; or by pouring zinc-filings through holes, in a plate of copper, upon a common electrometer; but the power of the combination may be most distinctly exhibited, in the experiments, called Gal vanic experiments; by connecting the two metals, which must be in contact with each other, with a nerve and muscle in the limb of an animal recently deprived of life, a frog, for instance; at the moment the contact is completed, or the circuit made, one metal touching the muscle, the other the nerve, violent contractions of the limb will be occasioned,

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543. The Galvanic apparatus consists of anarrow trough of earthenware, with grooves at cer tain distances, into which are slid alternately, plates of zinc and copper; and between each division, is poured a mixture of acid and water. If one hand be put to the plate of copper at the end of the trough, and another be put to the plate of zinc at the other end, a smart shock will be felt, and will be continued for a great th of time.

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Obs. 1.-The above represents an earthenware trough, with its plates, of separation, consisting, alternately, of copper and zinc, A wire is fixed to each end, for the purpose of conveying the stroke to the fat plate, or for any other desired purpose.

2.-The most powerful combination that exists, in which number of alternations is combined with extent of surface, is that constructed by the subscriptions of a few zealous cultivators and patrons of science, in the lada ratory of the Royal Institution. It consists of two had dred instruments, connected together in regular ordet each composed of ten double plates, arranged in cells of porcelain, and containing in each plate thirty-two square inches; so that the whole number of double plates is 2,000; and the whole surface 128,000 square inchei This battery, when the cells were filled with 60 parts of water mixed with one part of nitric acid, and one part of sulphuric acid, afforded a series of brilliant and im pressive effects. When pieces of charcoal, about an incl long and one-sixth of an inch in diameter, were brought near each other (within the thirtieth or fortieth part of an inch,) a bright spark was produced, and more than half the volume of the charcoal became ignited to white ness; and, by withdrawing the point from each other, a constant discharge took place through the heated air, in a space equal at least to four inches, producing nest brilliant ascending Arch of light, broad and conical in form in the middle, When any substance was introduced into this arch, it instantly became ignited; platin melted as readily in it as wax in the fame of a common candle; quarts, the sapphire, magnesia, lime, all entered ato fusion; fragments of diamond, and points of char

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coal and plumbago, rapidly disappeared, and seemed to evaporate in it. Such are the decomposing powers of electricity, that not even insoluble compounds are capable of resisting their energy; for even glass, sulphate of baryta, fluor spar, &c., when moistened and placed in contact with electrified surfaces from the Galvanic apparatus, are slowly acted upon, and the alkaline, earthy or acid matter, carried to the poles in the common order Not even the most solid aggregates, nor the firmest compounds, are capable of resisting this mode of attack; its operation is slow, but the results are certain; and sooner or later, by means of it, bodies are resolved into simpler forms of matter.-DAVY.

544. It is ascertained, that during these shocks an oxydation of the metallic plates takes place; and, after their surfaces become tarnished, the shock diminishes; but, ou being wiped, its force is renewed.

A combination of these troughs forms a galvanic battery, the force of which has produced the most surprising effects; and, by disturbing the close affinity of the constituent parts of many bodies, has led to the analysis of substances, hitherto deemed simple and elementary.

Obs. Some fishes, as the torpedo, the gymnotus electricus, and the silarus electricus, when touched, communicates shocks to, the human body like those of electrieicy twbut as there is no circuit for the Buid, in these cases monadequate solution has yet been found of this strange phenomenon,

0545. Since the identity of lightning and electric matter has been ascertained, philosophers have been led to seek the explication of aerial meteors imprinciples of electricity and there is no doubt, that the greater part of them, and especially the aurora borealis, are electrical, or gaseous phenomena.

It has been observed, that the aurora borealis
produces a very sensible fluctuation in the mag-
netic needle; and that the flashes have been at-
tended with various rumbling and hissing sounds
Now black, and deep, the night begins to fall,
Drear is the state of the benighted wretch,
Who then, bewilder'd, wanders through the dark,
Perhaps, impatient as he stumbles on,
Struck from the root of slimy rushes, blue,
The wildare scatters round, or gather'd, trails
A length of dame deceitful o'er the moss i
Whither, decoy'd by the fantastic blaze,
Now lost, and how renew'd, he sinks absorpt,
Rider and horse, amid the miry gulfi

At other times, gleaming on the horse's mane,
The meteor sits and shows the narrow path,
That winding, leads through pits of death 4 or else,
Instructs him how to take the dangerous ford,

LUOMION,

646. Earthquakes, the most dreadful pheno mena of nature, have been ascribed, by some naturalists, to water, fire, steam, and electricity; each of these powerful agents being supposed to operate in the bowels of the earth.

Subterraneous fire, and steam generated from it, are supposed to be the true causes of earthquakes. The elasticity of steam, and its expan sive force, are every way capable of producing the stupendous effects attributed to earthquakes; the force of steam being 28 times greater than that of gunpowder.

Can the poor, brittle tenements of man

Withstand the dread convulsion? Their dear homes,
(With shaking, tottering, crashing, bursting, fall,)
The boldest fly and, on the open plain,
Appall'd, in agony, the moment wate,

When, with disrupture vast, the waving earth
Shall 'whelm them in her sea-disgorging womb,

Nor, less affrighted, are the bestial kind :—
The bold steed quivers in each panting vein,
And staggers, bath'd in deluges of sweat -
The lowing herds forsake their grassy food
And send forth frighted, woful, hollow sounds
The dog, the trusty centinel of night,
Deserts his post assign'd, and piteous howls.

THOMSON.

547. The most remarkable changes in the form and constitution of the earth, since the deluge, have probably been produced by subterraneous fires in volcanoes, and by earthquakes; by which plains are converted into mountains, the ocean into islands, and dry land into pools.

Obs. Half a pound of steel-filings, half a pound of brimstone, and a pint of water, will, when well mixed, acquire heat enough to make the mass take fire: and it appears, that volcanic mountains abound in such mixtures; which are ignited, no doubt, by rain falling into their craters, or by the sea communicating with their bases and lower cavities.

The fluid lake that works below,
Bitumen, sulphur, salt, and iron-scum,
Heaves up its boiling tide. The lab'ring mount
Is torn with agonizing throes. At once,
Forth from its side, disparted, blazing pours
A mighty river; burning in prone waves,
That glimmer thro' the night, to yonder plain.
Divided there, a hundred torrent-streams,
Each ploughing up its bed, roll dreadful on,
Resistless. Villages, and woods, and rocks,
Fall flat, before their sweep.

MALLET.

548. The eruptions of volcanoes exhibit dreadful phenomena, in prodigious inundations of liquid fire, which bear inevitable destruction with them.

The name of lava is given to these fiery streams, consisting of a mixture of stones, sand,

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