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of the conjunctive wires, and the being founded upon Voltaic princircumstances under which they ciples, must be considered as probecame effective; he found, for perly falling under the head of his instance, that if a small steel bar electrical researches.

It appears be attached to the conjunctive that the Commissioners of the wire, and parallel to it, it does not Navy, impressed with the evil become a polar magnet; but that, arising from the destructive inif it be attached transversely, it fluence of sea-water upon the does become polar, and that it copper sheathing of ships of war, becomes north and south, or south applied to the Council of the and north, according to the Royal Society, in the hope that direction of the supposed elec- some plan might be suggested for tric current traversing the con- arresting, if not preventing, the junctive wire, as or the decay of so expensive an article. other end of it may be positive or Sir É. Davy charged himself with negative. “In viewing these phæ- the inquiry; and presented its nomena,” says sir Humphry, “a results in a paper which was read number of curious speculations before the society on the 22nd of cannot fail to present themselves January, 1824, and which was to every philosophical mind; such continued in another communicaas, whether the magnetism of the tion dated 17th of June, 1824, earth may not be owing to its and concluded in a third, read electricity, and the variation of 9th of June, 1825. We shall enthe needle to the alterations in the deavour to put the reader in poselectrical currents of the earth, in session of the principle facts consequence of its motions, in- elicited by this inquiry. Davy ternal chemical changes, or its had advanced the hypothesis, that relations to solar heat; and whe- chemical and electrical changes ther the luminous effects of the were identical, or dependent upon auroras at the poles are not shown the same property of matter; and by these new facts to depend on he had shown that chemical atelectricity.” It is certainly evi- tractions may be exalted, modident, that, if strong electrical fied, or destroyed, by changes in currents be supposed to follow the the electrical states of bodies ; apparent course of the sun, the that substances will combine only magnetism of the earth ought to when they are in different electribe such as it is actually found to cal states; and that, by bringing be; and to afford a popular illus- a body, naturally positive, artitration of this theory, sir Hum- ficially into a negative state, its phry directed a sphere to be con- usual powers of combination are structed, in which arrangements altogether destroyed : it was, in were made for passing the electric short, by an application of this cities, from the two ends of the very principle that he decombattery, in the direction of the posed the alkalies; and it was ecliptic, upon which the poles from the same energetic instruwere found to become magnetic. mentality that he now sought a

Sir H. Davy's method for prevent- remedy for the rapid corrosion of ing the corrosion of the copper copper sheathing. Let us sheathing of ships by sea-water, how dexterously he grappled with Vol. LXXI.

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the difficulties of his subject. was encouraged to proceed; and When a piece of polished copper the results were of the most satisis suffered to remain in sea-water, factory kind. A piece of zinc, as the first effects are, a yellow tarn- large as a pea, or the point of a ish

upon the surface, and a cloudin small iron nail, was found fully ness in the water, which take adequate to preserve forty or fifty place in two or three hours: the square inches of copper ; and this, hue of the cloudiness is at first wherever it was placed, whether white, and it gradually becomes at the top, bottom, or in the midgreen. In less than a day a

dle of the sheet of copper, and bluish-green precipitate appears whether the copper was straight in the bottom of the vessel, which or bent, or made into coils. And constantly accumulates; thisgreen where the connection between the matter appears principally to con- different pieces of copper was sist of an insoluble compound of completed by wires, or thin filacopper (a sub-muriate) and hy- ments of the fortieth or fiftieth of drate of magnesia. Reasoning an inch in diameter, the effect upon these phenomena, Davy ar- was the same; every side, every rived at the conclusion that cop- surface, every particle of the copper could act upon sea-water only per remained bright, whilst the when in a positive state ; and since iron, or the zinc, was slowly corthat metal is only weakly positive roded. A piece of thick sheet in the electro-chemical scale, he copper, containing, on both sides, considered that, if it could be about sixty square inches, was cut only rendered slightly negative, in such a manner as to form seven the corroding action of sea-water divisions, connected only by the upon it would be null. But how smallest filaments that could be was this to be effected ? At first, left, and a mass of zinc, of the he thought of using a Voltaic bat- fifth of an inch in diameter, was tery; but this could hardly be ap- soldered to the upper division. plicable in practice : he next The whole was plunged under seathought of the contact of zinc, water; the copper remained pertin, or iron; but he was prevented fectly polished. The same exfor some time from trying this, by periment was made with iron ; the recollection that the copper in and after the lapse of a month, in the Voltaic battery, as well as the both instances, the copper was zinc, was dissolved by the action found as bright as when it was of dilute nitric acid; and by the first introduced, whilst similar fear that too large a mass of ox- pieces of copper, undefended, in idable metal would be required to the same sea-water, underwent produce decisive results. After considerable corrosion, and proreflecting, however, for some time duced a large quantity of green on the slow and weak action of deposit in the

bottom of the sea-water on copper, and the small vessel. Numerous other difference which must exist be- periments were performed, and tween their electrical powers, and with results equally conclusive knowing that a very feeble chemi- of the truth of the theory which cal action would be destroyed by had suggested them. It remained a very feeble electrical force, he only that the experiments should

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be conducted on a large scale. rine insects has been favoured, The lords commissioners of the and the ships, thus defended by Navy accordingly gave sir Hum- iron or zinc, have become so foui, phry permission to ascertain the as scarcely to continue navigable. practical value of his discovery by This would seem to depend upon trials upon ships of war; and the several causes, especially upon the results, to use his own expression, deposition of saline and calcareous even surpassed his most sanguine matter, arising from the decomexpectations. Sheets of copper, position of marine salts. Whether defended by from 1-40th to 1- or not his principles can be ren1000th part of their surface of dered subservient to the protection zinc, malleable and cast iron, of copper sheathing, it must at were exposed, for many weeks, in least be admitted, that the results the flow of the tide in Portsmouth obtained by him are of the most harbour, their weights having been interesting description, and capaascertained before and after the ble of various useful applications. experiment. When the metallic By introducing a piece of zinc, or protector was from 1-40 to 1-110, tin, into the iron boiler of the there was no corrosion nor decay steam-engine, we may prevent of the copper; with small quan- the danger of explosion, which tities it underwent a loss of weight. generally arises, especially where The sheathing of boats and ships, salt-water is used, as in those of protected by the contact of zinc, steam-boats, from the wear of one cast and malleable iron in different part of the boiler, Another improportions, compared with that portant application is in the preof similar boats and sides of ships vention of the wear of the paddles, unprotected, exhibited bright sur- or wheels, which are rapidly disfaces, whilst the unprotected cop- solved by salt water. Mr. Pepys per underwent rapid corrosion, has extended the principle, for the becoming first red, then green, preservation of steel instruments, , and losing a part of its substance by guards of zinc; and razors and in scales. Is it not, then, a fact, lancets have been thus defended established beyond all controversy, with perfect success, that small quantities of electro- In the year 1805, Mr. Davy positive metals will prevent the was elected a member of the corrosion or chemical changes of Royal Irish Academy; and locopper exposed to sea-water; and wards the close of the year 1810, that the results appear to be of he delivered a course of lectures the same kind, whether the ex- before the Dublin Society, and periments are made upon a minute received from Trinity College, scale, and in contined portions of Dublin, the honorary degree of water, or on large masses, and in LL.D. the ocean? How, then, has it In 1812 Mr. Davy married. happened, that this scheme of The object of his choice was Jane, protection has not been adopted ? daughter and heiress of Charles Simply, because, in overcoming Kerr, of Kelso, esq., and widow of one evil, another has been created; Shuckburgh Ashby Apreece, esq., by protecting the copper, the ac- eldest son of the present sir cumulation of sea-weeds and ma- Thomas Hussey Apreece, bart.

By his union with this lady, Mr. buretted hydrogen gas : but its Davy acquired a considerable relations to combustion had not fortune. On the 9th of April, been examined. It is chiefly proonly two days previously to his duced from what are called blowmarriage, he received the honour ers or fissures in the broken strata, of knighthood from the Prince near dykes. Sir Humphry made Regent, being the first person on various experiments on its comwhom his Royal Highness conferred bustibility and explosive nature; that dignity.

and discovered, that the fire-damp The frequency of accidents, requires a very strong heat for its arising from the explosion of the inflammation; that azote and carfire-damp, or inflammable gas, of bonic acid, even in very small prothe coal mines, mixed with at- portions, diminished the velocity mospherical air, occasioned the of the inflammation ; that mixture formation of a committee at Sun- of the gas would not explode in derland, for the purpose of in- metallic canals or troughs, where vestigating the causes of these their diameter was less than one calamities, and of endeavouring seventh of an inch, and their to discover and apply a preventive. depth considerable in proportion Sir Humphry received an invita- to their diameter; and that extion, in 1815, from Dr. Gray, one plosions could not be made to pass of the members of the committee; through such canals, or through in consequence of which he went very fine wire sieves, or wire gauze. to the north of England, and The consideration of these facts visiting some of the principal led sir Humphrey to adopt a collieries in the neighbourhood of lamp, in which the flame, by being Newcastle, soon convinced him- supplied with only a limited self that no improvement could quantity of air, should produce be made in the mode of ventila- such a quantity of azote and cartion, but that the desired pre- bonic acid as to prevent the exventive must be sought in a new plosion of the fire-damp, and method of lighting the mines, free which, by the nature of its aperfrom danger, and which, by in- tures for giving admittance and dicating the state of the air in the egress to the air, should be renpart of the mine where inflamma- dered incapable of communicating ble air was disengaged, so as to any explosion to the external air. render the atmosphere explosive, These requisites were found to be should oblige the miners to retire afforded by air-tight lanterns, of till the workings were properly various constructions, supplied cleared. The common

means with air from tubes or canals of then employed for lighting the small diameter, or from aperdangerous part of the mines con- tures covered with wire-gauze, sisted of a steel wheel revolving placed below the flame, through in contact with flint, and affording which explosions cannot be coma succession of sparks : but this municated, and having a chimney apparatus always required a per- at the upper part, for carrying off son to work it, and was not en- the foul air. Sir Humphry soon tirely free from danger. The fire. afterwards found that a constant damp was known to be light car- flame might be kept up from the explosive mixture issuing from of the Institute of France, and the apertures of a wire-gauze vice-president of the Royal Instisieve. He introduced a very small tution. - He was created a baronet, lamp in a cylinder, made of wire- October 20, 1818. In 1820, he gauze, having six thousand four

was elected a foreign associate of hundred apertures in the square the Royal Academy of Sciences inch. He closed all apertures ex- at Paris, in the room of his councept those of the gauze, and intro- tryman Watt; and in the course duced the lamp, burning brightly of a few years, most of the learned within the cylinder, into a large bodies in Europe enrolled him jar, containing several quarts of among their members. the most explosive mixture of gas Much of this period of his life from the distillation of coal and was spent in visiting different air ; the fame of the wick im- parts of Europe for scientific purmediately disappeared, or rather poses. He analysed the colours was lost, for the whole of the in- used in painting by the ancient terior of the cylinder became Greek and Roman artists. His filled with a feeble but steady experiments were chiefly made on fame of a green colour, which the paintings in the baths of Titus, burnt for some minutes, till it had the ruins called the baths of Livia, entirely destroyed the explosive in the remains of other palaces power of the atmosphere. This and baths of ancient Rome, and discovery led to a most important in the ruins of Pompeii. By the improvement in the lamp, divested kindness of his friend Canova, the fire-damp of all its terrors, who was charged with the care of and applied its powers, formerly the works connected with ancient so destructive, to the production art in Rome, he was enabled to of a useful light. Some minor select, with his own hands, speciimprovements, originating in sir mens of the different pigments Humphry's researches into the that had been found in vases disnature of flame, were afterwards covered in the excavations which effected. Experiments of the had been lately made beneath the most satisfactory nature were ruins of the palace of Titus, and speedily made, and the invention to compare them with the colours was soon generally adopted. Some fixed on the walls, or detached in attempts were made to dispute the fragments of stucco. The results honour of this discovery with its of all these researches were pubauthor, but his claims were con- lished in the Transactions of the firmed by the investigations of the Royal Society for 1815. On his first philosophers of the age. The examination of the Herculaneum coal-owners of the Tyne and Wear manuscripts at Naples, in 1818-19, evinced their sense of the benefits he was of opinion they had not resulting from this invention, by been acted upon by fire, so as to presenting sir Humphry with a be completely carbonized, but handsome service of plate, worth that their leaves were cemented nearly 2,0001., at a public dinner together by a substance formed duat Newcastle, October 11th, 1817. ring the fermentation and chemi

In 1813, sir Humphry was cal change of ages. He invented elected a corresponding member a composition for the solution of

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