owing to the infusible nature of the earths: the strong affinity of their bases for oxygen made it unavailing to act upon them in solution in water: and the only methods that proved successful, were those of operating upon them by electricity in some of the combinations, or of combining them at the moment of their decomposition by electricity, in metallic alloys, so as to obtain evidences of their nature and properties. It is impossible to follow the philosopher through all the intricate paths of this investigation: suffice it to say, that, although he was unable to produce the metallic bases of the earths in the same unequivocal form as he produced those of the alkalies, he furnished sufficient evidence of their being metallic oxides.

What an immense step was thus made in the investigation of Nature! In sciences kindred to chemistry, the knowledge of the composition of these bodies, and the analogies arising from it, have opened new views, and led to the solution of many problems. In geology, for instance, has it not shown. that agents may have operated in the formation of rocks and earths, which have not hitherto been supposed to exist? It is evident that the metals of the earths cannot exist at the surface of our globe, but it is very probable that they may constitute a part of its interior; and such an assumption would at once offer a plausible theory for the phænomena of volcanoes, the formation of lavas, and the excitement and effects of subterraneous heat, and might even lead to a general hypothesis in geology. At a subsequent period, our illustrious chemist followed the subject up by numerous observations and experiments in a volcanic country. Whoever witnessed it, must remember with delight the beautiful display of his theory, as exhibited in an artificial volcano on the table of the Royal Institution. A mountain was modelled in clay, and a quantity of the "metallic bases" introduced into its interior; on water being poured upon it, the metals were soon thrown into violent action successive explosions were produced-boiling lava was seen flowing down its sides from a crater in miniature - mimic lightnings played around

and the tumultuous applause of the audience might almost, in the instant of dramatic illusion, have been mistaken for the shouts of the alarmed fugitives of Herculaneum or Pompeii.

Sir Humphry Davy's Bakerian Lecture of 1808, entitled, "An Account of some new Analytical Researches on the Nature of certain Bodies, particularly the Alkalies, Phosphorus, Sulphur, Carbonaceous Matter, and the Acids hitherto undecomposed; with some general Observations on CHEMICAL THEORY," abounds in elaborate experiments with the Voltaic apparatus, made with the hope of extending our knowledge of the principles of bodies, by the new powers and methods arising from the application of electricity; but although it furnishes results of great interest, and records phænomena which may serve as guides in future enquiries, still it cannot be said to have astonished the chemical world by any brilliant discovery; and yet it announced the decomposition of boracic acid, and the developement of its inflammable base at the negative surface of the battery, a discovery which, at any other period, would have produced great excitement in the chemical world; but the fact is, that the splendour of his former lecture, like the blaze of the sun, left our organs of perception incapable of receiving a just impression from any lesser light.

In reviewing his several memoirs upon Voltaic electricity, we have illustrated the original, cautious, and yet intrepid advances of his mind; we are now about to notice a series of papers which manifest the zeal and industry with which he pursued the track of others. The similarity of the laws of electrical and magnetical attraction had long excited the attention of the philosopher, and numerous had been the attempts to establish the existence of an identity, or intimate relation, between these two forces; but little light had been thrown upon the subject before the year 1819, when M. Oersted, Secretary to the Royal Society of Copenhagen, published an account of some experiments exhibited in his lecture before the University, by which it was demonstrated that the magnetic needle was moved from its position by the action of

the Galvanic apparatus. And it may be here necessary to state, that these experiments, unlike all preceding ones, were made with the two ends of the pile in communication with each other; to which circumstance are to be attributed the novel results that followed. In pursuing the investigation with a more powerful battery, M. Oersted fully ascertained that the phænomena exhibited by the needle did not depend upon electrical attraction and repulsion, for its movements were wholly at variance with such an explanation; they must depend, then, upon the production of a new energy, generated by the action of the two electricities thus brought into conflict, and which, if not identical with, must be nearly related to magnetism! It moreover appeared probable from the motions of the magnet, when differently placed with regard to the conjunctive wire, or that wire by which the opposite ends of the battery were connected, that this energy circulated, or performed a circular movement around the axis of the conductor, and thus drove the magnetic pole towards the east or west, according to the direction of the needle with reference to such a current. No sooner had this extraordinary discovery been announced in this country, than Sir Humphry Davy proceeded to repeat the experiments, and with his characteristic talent, to vary and extend them. The nature and limits of this memoir will not allow us to follow him it is sufficient to say, that he obtained new results, and expanded the views which Oersted had opened. He particularly investigated the magnetizing powers of the conjunctive wires, and the circumstances under which they became effective he found, for instance, that if a small steel bar be attached to the conjunctive wire, and parallel to it, it does not become a polar magnet; but that, if it be attached transversely, it does become polar, and that it becomes north and south, or south and north, according to the direction of the supposed electric current traversing the conjunctive wire, as one or the other end of it may be positive or negative. viewing these phænomena," says Sir Humphry, "a number of curious speculations cannot fail to present themselves to

“In

every philosophical mind; such as, whether the magnetism of the earth may not be owing to its electricity, and the variation of the needle to the alterations in the electrical currents of the earth, in consequence of its motions, internal chemical changes, or its relations to solar heat; and whether the luminous effects of the auroras at the poles are not shown by these new facts to depend on electricity." It is certainly evident, that, if strong electrical currents be supposed to follow the apparent course of the sun, the magnetism of the earth ought to be such as it is actually found to be; and to afford a popular illustration of this theory, Sir Humphry directed a sphere to be constructed, in which arrangements were made for passing the electricities, from the two ends of the battery, in the direction of the ecliptic, upon which the poles were found to become magnetic.

In accordance with the plan originally proposed for the review of Davy's labours, we shall next offer an account of his method for preventing the corrosion of the copper sheathing of ships by sea-water; which being founded upon Voltaic principles, must be considered as properly falling under the head of his electrical researches. It appears that the Commissioners of the Navy, fully impressed with the evil arising from the destructive influence of sea-water upon the copper sheathing of his Majesty's ships of war, applied to the Council of the Royal Society, in the hope that some plan might be suggested for arresting, if not for preventing, the decay of so expensive an article. Sir H. Davy charged himself with the enquiry; and presented its results in a paper which was read before the Society on the 22d of January, 1824, and which was continued in another communication dated 17th of June, 1824, and concluded in a third, read 9th of June, 1825. We shall endeavour to put the reader in possession of the principal facts elicited by this enquiry. We have already stated, that Davy had advanced the hypothesis, that chemical and electrical changes were identical, or dependent upon the same property of matter; and that he had shown that chemical attractions may be exalted, modified, or destroyed, by changes

in the electrical states of bodies; that substances will only combine when they are in different electrical states; and that, by bringing a body, naturally positive, artificially into a negative state, its usual powers of combination are altogether destroyed: it was, in short, by an application of this very principle that he decomposed the alkalies; and it was from the same energetic instrumentality that he now sought a remedy for the rapid corrosion of copper sheathing. Let us see how dexterously he grappled with the difficulties of his subject. When a piece of polished copper is suffered to remain in sea-water, the first effects are, a yellow tarnish upon the surface, and a cloudiness in the water, which take place in two or three hours: the hue of the cloudiness is at first white, and it gradually becomes green. In less than a day a bluish-green precipitate appears in the bottom of the vessel, which constantly accumulates; this green matter appears principally to consist of an insoluble compound of copper (a sub-muriate) and hydrate of magnesia. Reasoning upon these phenomena, Davy arrived at the conclusion that copper could act upon sea-water only when in a positive state; and since that metal is only weakly positive in the electrochemical scale, he considered that, if it could be only rendered slightly negative, the corroding action of sea-water upon it would be null. But how was this to be effected? At first, he thought of using a Voltaic battery; but this could hardly be applicable in practice: he next thought of the contact of zinc, tin, or iron; but he was prevented for some time from trying this, by the recollection that the copper in the Voltaic battery, as well as the zinc, was dissolved by the action of dilute nitric acid; and by the fear that too large a mass of oxidable metal would be required to produce decisive results. After reflecting, however, for some time on the slow and weak action of sea-water on copper, and the small difference which must exist between their electrical powers, and knowing that a very feeble chemical action would be destroyed by a very feeble electrical force, he was encouraged to proceed; and the results were of the most satisfactory kind. A piece of zinc, as