performance of the compass, is this. The vessel is what is technically called 'swung,' as soon as it is ready for sea, with its compasses on board. Its head is turned into all possible directions, while some land object is still kept in sight to indicate what the precise position at any moment is, and the deviation of the compass from its proper bearing in each position is marked and recorded. The record is then preserved, to be employed as a check upon the compass in the future. In the working of the ship, the error for each position is allowed for; and so the mariner manages to direct his path aright by an erroneously pointing guide. This method of swinging vessels, for the ascertainment of their compass-errors, answered very well so long as only wooden ships were employed. Now, however, when the largest vessels are built entirely of iron, it unfortunately becomes of very little service. These vast iron structures start upon their marine existence with magnetic dispositions which can be accurately ascertained and allowed for. But, alas, these dispositions, most strange to say, are as capricious as the winds and the waves, which are to be their playmates. Every time the vessel encounters the shock of heavy waves, having its head turned towards a new point of the compass, the great terrestrial magnet beneath gets a different pull upon its contained magnetism, and the poles of its contained magnets shift their positions, producing a correspondent change of deviation in the compassneedles. It is found that even the long continued tremor set up by the working of steam-machinery, in a comparatively smooth sea, will produce this alteration of deviation, when a new course has been suddenly shaped. Nay, the mere passage near to a prominent headland of the coast, which is itself in a state of induced magnetism, in consequence of some peculiar arrangement of its own parts, may effect the same momentous change. The captain of one of the Cunard line of Atlantic steamers told Dr. Scoresby, in the spring of 1848, that he always remarked on rounding a prominent headland in the south-east of Ireland, on the return-voyage from America, that his compass-cards swung widely,' and sometimes went quite round. Captain Moresby, the intelligent commander of the Ripon,' states that the compass-variation commonly changes four or five degrees on passing Cape Bon, near Tunis, and does not resume its normal amount until after some hours. It is probably sometimes the direct magnetic influence of one of the constituents of the rocky masses of the coast, which seduces the compass-needle from its sober terrestrial allegiance. But, more generally, it is the influence of the coast acting upon the retentive magnetism of the ship, which produces the disturbance. In this case, that it is so is obvious from its being only the compasses of iron ships that are obnoxious to the derangement. 6 6 It is a very curious fact, that practical seamen had learned to make allowance for compass-deviations, induced by the proximity of certain coasts, long before any thing was known of the nature of inductive magnetism. Dr. Scoresby alludes to one very striking instance of this in his second volume of Mag'netical Investigations.' On the 18th of December, in the year 1811, the line-of-battle-ship, 'Hero,' left Wingo Sound in the Cattegat, with a convoy of 120 sail of merchant-ships and transports under its charge. The vessel took a direct compasscourse for the Downs, from the coast of Denmark, and in the middle of the night of the 23rd, went on shore, in a heavy squall of wind and sleet, upon a sand off the Island of Texel. Two other line-of-battle-ships, the St. George' and the 'Defiance,' which were some distance behind the Hero,' and steering the same course, were driven on shore, on the coast of North Jutland, in the same gale, and several of the Hero's' convoy followed the Hero's' lead, and shared the same fate. On the evening of the 23rd, at the commencement of the gale, a Whitby pilot, who had charge of the Centurion' transport, was down in the cabin taking a meal, when he was told that the commodore on board the Hero' was signalling to steer south-southwest. On the instant the wary seaman issued the order ‘Haul our ship to the south-west!' and then added in a solemn tone to the officers who were around him in the cabin, 'If the com'modore stands that way' (so little towards the west), 'they will all sleep in their shoes before the morning.' The opinion of the old pilot was sadly justified by facts. Before the morning nearly two thousand men were sleeping in their shoes' beneath the surf of the German Ocean. Only those vessels that followed the example of the Centurion' escaped from the storm. When the captain of the Hero' became aware that he was approaching some shoal, he actually ordered the ship to be steered southsouth-east, directly in the teeth of the danger, in the conviction that he must be entangled somewhere with the British coast. The commanders of the line-of-battle-ships, placing their faith, no doubt, in the scientific light which they then possessed, took the compass for their sole guide, and followed it to destruction. The Whitby pilot, on the other hand, had been taught by experience, while making this passage, that something always tended to carry the ship towards the Dutch coast, and accordingly took care to give it what the more scienti fically trained officers of the navy would, no doubt, have considered an unnecessarily wide berth. In consequence of the recent largely extended use of iron in the construction of ships, it has become a consideration of most momentous import, to find some means whereby the uncertain and capricious compass-deviations, incident to the employment of the metal, may be obviated. The Astronomer Royal has devised a plan which is attended with a considerable measure of success, so long as the vessel moves only through a narrow range of latitude, and so long as it is not exposed to much mechanical violence. This method is to place fixed magnets near to the compasses, in such a position that they exactly undo what the magnetic masses of the ship accomplish. Then the compassneedles are left free to range in exact obedience to the directive force of the earth's polarity. Dr. Scoresby, however, who had perhaps a more intimate practical knowledge of this subject than any other man, distrusted the Astronomer Royal's method. He thought that the Astronomer Royal entirely under-estimated the power of accidental mechanical impulse to render iron vessels susceptible to changes of magnetic condition, and maintained that the compensating method needs to be itself subjected to frequent corrections, as these changes arise, before it can be admitted as trustworthy. This being a process that would be found to be very difficult in application to vessels at sea, Dr. Scoresby himself proposed the adoption of a very much more simple contrivance, which he believed to be perfectly effectual under all circumstances. It is merely to keep a standard compass some distance up aloft, with which the working compasses may be frequently compared. The deranging influence of the magnetism of the vessel takes effect mainly because the compass is so near to the metallic masses of the ship. If the compass be removed to some considerable distance from these masses, then their power becomes comparatively trifling, when measured with the influence of the earth, which is not diminished in like degree, on account of the stupendous mass of the terrestrial sphere. Upon one occasion Dr. Scoresby found that when every compass on the saloon-deck of the large iron vessel, the Imperador,' was in error from two and a half to three and a half points, a compass raised thirty-two feet above the deck was absolutely true in every position in which the vessel was placed. The veteran navigator and philosopher undertook a voyage to Australia, shortly before his decease, exclusively to test the efficacy of his plan, and he had the satisfaction of finding it answer his expectations in the most complete way. His opinion was subsequently expressed, that with a standard-com pass aloft, and with a fair measure of precaution, in making frequent references to it, even an iron steam-ship may go any where and do any thing, without incurring the risk of being misled by the capricious conditions of its own metallic mass. - The distinguished French philosopher M. Ampère, long since maintained that the magnetism of the earth was due to the presence of electrical currents coursing round its spheroidal mass, at a small depth below the surface, and from east to west. A full investigation of the causes which could give rise to such a series of equatorially moving currents, as well as of the evidence that is available to prove that such currents are actually in existence, is made in the third volume of M. De la Rive's work, and the judicial summing up is there in favour of M. Ampère's notion. The huge earth, for ever rotating on an axis in virtue of some primeval necessity impressed upon its spheroidal form, with its circling currents of electrical force coursing round its equatorial girdle,—and with its polar tensions of magnetic force radiating from near the extremities of its axis, seems to be but a copy in large of the invisible material atom which is the basis of its own substance. And this, in all probability, is not the final suggestion Electrical Science is destined to furnish in this direction. There are dull molecules and bright molecules upon the earth, and dull masses and brightly glowing masses, -illuminated worlds and illuminating suns, in the wide spaces of the heavens. The dull molecules of terrestrial matter become resplendent with light, when their rotatory movements are quickened by the spur of electrical tension.-Why are the stellar orbs of the remote Universe so brilliant? This much at least may be said. The stars blaze with the same illumination that sparkles in the earth. The light which ripples upon the shore of the infinite, is the same light which bursts from the morsel of charcoal when the electrician touches it with his energising wires. It is bent by the prism, collected by the lens, and reflected by the mirror in precisely the same way. It produces the same changes on the sensitive plate of the photographist, and the same feeling on the sensitive membrane of the organ of vision. The sagacity which is now on the point of demonstrating that the earth is a huge electro-magnet, inductively excited by the sun, already suspects that the inductively exciting sun, and the kindred stars, are themselves, in their surpassing splendours, vast electric lights. ART. III.- Mémoires du Duc de Raguse; de 1792 à 1832. 9 vols. 8vo. Paris: 1857. MARSHAL MARMONT for by that name the Duke of Ragusa will probably be best known to posterity bequeaths these remarkable Memoirs to the world in the following terms: — 'Two things have chiefly occupied my mind in these latter years: the compilation of the memoirs of my life, and the narrative of my travels in 1834 and 1835. I had imposed on myself the obligation of completing the first work before leaving Vienna in 1834, and I have accomplished it; for I looked on it as a duty, before encountering any new risks, to place beyond all hazard a publication which must have some weight in the History of my Time. I am the only survivor among those who surrounded, at the outset of his career, the extraordinary man who has weighed so powerfully on his age; none of those who occupied the same position as myself at his side have written; my words, therefore, will be received for truth. And I hope that the spirit of veracity which animates me will give a deserved credit to my writings in the eyes of posterity. Having been from a very early age an actor in the greatest events of that fabulous period of eighteen years, during which so many almost incredible prodigies succeeded each other, until still greater evils came to close it, I have seen much as regards both things and men. Furnished by nature with a good memory, and, by a singular good fortune, not having lost a single important paper, I have been able to retrace facts as they were. All the events are still present to my mind. The reading of these memoirs will therefore serve to enlighten the student as to the value of the declamations of that crowd of charlatans with whom our epoch and our country abound, and who change and modify their language to serve the circumstances of the times and the interests of the day.' (Memoirs, vol. ix. p. 1.) From the editor's introduction to these volumes we learn that the writer began to compile them in 1828, and continued to work on them until his death. They bear in consequence evident marks of having been written at various epochs, and of having undergone a great deal of addition and retouching. The editor affirms that he has scrupulously obeyed the Marshal's solemn injunction, de les publier sans y apporter aucun changement, même sous le prétexte de correction de style: et ne 'souffrir ni augmentation dans le texte, ni diminution, ni sup'pression quelconque.' It would ill become us, members of the critical profession, to complain of the extraordinary affluence of materials for the history of the last generation which are now accumulating in our hands. We have scarcely digested the very important and |