de eque of place the upper part of the limbs between a pennypiece and a half-crown piece, taking care that the metals are in contact at the top-if one of them be in contact with the muscle, and the other be depressed, so as to touch the nerve, the contractions will be observed as before. This kind of excitability is retained much longer by cold-blooded animals after death, than by others, and they are affected by states of electricity so feeble as not to be indicated by the most delicate electrometers. A feeble spark, or the most trifling charge of a Leyden jar, is sufficient for the above experiment. It may also be performed with a live flounder, by placing it in a plate upon a slip of zinc, and putting a shilling on its back; then with a piece of wire connected with the zinc make Occasional contacts upon the shilling, and at each contact strong muscular contractions are produced. A similar result is obtained with live worms, leeches, &c. The unpleasant sensations which these animals are thus made to endure, may be received by the following simple experiment :-place a half-crown piece upon the tongue, and a penny-piece below it; no effect is produced while the metals are not in contact; but if we make them touch, a peculiar sharp, arid taste is perceived, and with some persons a flash of light passes before the eyes. We have already given the hypothesis whereby Galvani sought to explain the above phenomena, but it was controverted by the celebrated Volta, professor of natural philosophy, at Pavia, who showed that the effect depended upon the contact of dissimilar metals, and not upon the connection made between different parts of an animal. He showed that contractions could not be excited by the application of two pieces of the same metal, and he referred the effect when different metals were employed to what is termed the electro-motive power of dissimilar metals. If, for example, two discs of metal, one of zinc and the other of copper, be affixed at their centres to glass handles, and be placed in contact, they are found to be oppositely electrified: when they are removed from each other's influence, the zinc is found to be positive and the copper negative: hence it seems that a portion of electricity has passed from the lesser to the more oxidable metal, and this passage, or transfer, the nerve or muscle of the frog indicates in a very sensible manner. The chemical properties of metals are much influenced by this disturbance of electricity. For example:-if we hold a strip of silver, and another of zinc, in a test glass containing dilute sulphuric acid, so that the metals do not touch each other, the zinc only will be attacked by the acid, but if we bring the two metals into contact, the silver will immediately become active, and a stream of hydrogen gas will proceed from both metals. The experiment may also be varied by employing a weak solution of sulphate of copper. Place in it a strip of clean iron and another of silver, keeping them separate. The former will soon be coated with copper, and the latter will remain clean and bright, but if the strips be brought into contact, the silver will also acquire a cupreous coating. It is to the genius and industry of Volta that we owe the first galvanic apparatus; and we may almost say, that Although to Galvani belongs the glory of the first discovery of the site whereon to erect the noble superstructure of this beautiful science, yet Volta must be considered as the architect who drew the plans, laid the foundation, and assisted in the erection of one of the proudest monuments of modern science. The voltaic pile, so called in honour of its illustrious discoverer, we shall describe hereafter. We may here remark that the identity between common and voltaic electricity is now susceptible of demonstration. These two electricities are excited under different conditions, and they act in different manners. The effects of common electricity are produced by the accumulation of small quantities of the fluid brought into an insulated state, and exerting a high intensity, as shown by its attractive and repulsive forces, and its mechanical action upon non-conducting substances, whereas voltaic electricity may be developed in large quantity, but it cannot be accumulated so as to attain a high degree of tension, and its effects are produced while it flows in a continuous current along cinductors, or on a substance placed between two conductors. If for example we charge a Leyden jar, and then discharge it by means of the discharging rod, the intensity of the discharge will depend upon the extent to which the electricity has accumulated on the interior of the jar, and this again depends upon the time which it has been in connection with the prime conductor of the electrical machine in action; that is, supposing we do not in any case give the jar its full charge. The quantities of electricity sent into it may be indicated by an electrometer attached to the top of the jar. On discharging the jar there will be an explosion, and equilibrium will be immediately established. This, however, is by no means the case with voltaic electricity: there is no accumulation, and, consequently, no discharge: the fluid passes along in currents, and exerts its peculiar action when those currents are interrupted by the interposition of bad conductors. Voltaic currents are simple and compound. In the former case they exist in their most elementary form, and the latter are produced by a series of simple currents or circles acting in mutual connection. A simple voltaic circle may be formed by immersing two different metals in a dilute acid, and making them communicate by contact at the top, as in the figure, or Fig. 2. ZAS by attaching wires to the upper ends, and placing the wires in contact. Of the two metals one should be easily acted on by the acid, and the other with greater difficulty or not at all. The greater the dissimilarity in this respect, the more energetic will be the resulting electrical effects. In the figure, z represents a plate of zinc, and s is one of silver, partly immersed in very dilute sulphuric acid, and in contact at their upper ends: by such arrangement a current of electricity appears to be put in motion, passing from the zinc to the acid, from the acid to the silver, and from the silver again to the zinc, as shown by the direction of the arrows. If the metals are connected by means of wires, as shown in fig. 3, the circuit may be extended, and by one before described is, that the current can be intercepted and operated with by placing a substance at A, and closing* the current upon it. In the foregoing arrangements the wire B, attached to the silver plate, conveys'electricity to the wire c, attached to the zinc plate: B, therefore, is called the positive pole, because the electric current flows in a continual circuit, passing from the zinc to the acid, from the acid to the silver, and along the wires back to the zinc, so that we may suppose the wire в to be continually imparting electricity to the wire c: hence, the latter is the negative pole, and, according to the theory of the two fluids, a current of negative electricity ought to set in, in an opposite direction: but it will be convenient for us hereafter to trace the progress of the + or positive current only, not forgetting, however, that the transfer of any quantity of electricity in one direction implies the transfer of a similar quantity of or negative electricity in an opposite direction. с The simple voltaic circle last described may be conveniently modified by interposing a piece of flannel, dipped in dilute acid, between a plate of copper and one of zinc, instead of immersing the metals in the acid solution; or the copper may be shaped into the form of a vessel for containing the acid, and the zinc plate may be suspended in it, care being taken to support the latter by means of cork, to prevent the two metals from coming in contact. There is also another useful modification of the simple circle. c is a vessel Fig. 1. formed of two cylinders of sheet copper, placed one within the other, and closed at the bottom. is a cylinder of zinc, with a few pieces of cork attached, to prevent it from touching the interior sides, a a a, of the copper vessel, when it is placed between them. bb are small copper cups soldered on to conducting wires, and containing a little mercury, for the purpose of conveniently making the circuit, by the insertion of wires into the cups, or breaking it by removing them. The zinc cylinder being placed between the copper cylinders, and dilute acid being poured in, a simple galvanic circle is formed the moment metallic connection is made between the two little cups. z however, the current gives an additional effect to the affinity of one of the metals for some element in the liquid employed, and the affinity of the other metal for any one of the elements in the liquid is proportionally diminished. When a piece of zinc and another of copper are brought into contact in dilute acid, the zinc oxidizes more and the copper less rapidly than without such contact. This principle was applied by Sir Humphry Davy to the preservation of the copper sheathing of ships. If a sheet of copper be immersed in sea-water, or in a solution of common salt, it becomes rapidly corroded, and an oxy-chloride of copper is generated. The vessel containing the copper and the solution must be exposed to the air, of which a notable quantity is always taken up by water exposed to it. In this case, therefore, the oxygen of the air so absorbed by the water, unites with a portion of the copper, and with the sodium of the salt; the latter, being composed of sodium and chlorine, gives chlorine to another portion of the copper, and the oxide and chloride of copper thus formed combine. But if the copper be in contact with zinc, or some metal more readily oxidizable than copper, it is alone acted on, and the copper is preserved. In this way the copper sheathing of ships may be preserved, and the quantity of zine necessary to form a preservative voltaic circle with the copper is exceedingly small. A piece of zinc no larger than the head of a small round nail is sufficient to preserve between forty and fifty square inches of copper, the surface of which remains quite bright, while the zinc only is corroded. When, however, the copper is thus rendered an electro-negative body it beconies attractive of metals and their oxides and other compounds, which, as respects the protected copper, are electro positive bodies: among such are the earthy bodies contained in sea-water, such as lime, magnesia, and their compounds: when, therefore, a ship covered with protective copper was put to sea, the copper was soon covered with a crust of earthy matter, which acted as an additional preservative, but gave rise to a new and unforeseen difficulty: sea-weeds and a variety of marine animals attached themselves so abundantly to the ship's bottom as to impede the sailing of the vessel, and thus this beautiful application of galvanic science was necessarily abandoned. THE false modesty of the insignificance of such a being as man has always encouraged modern unbelievers to call in We have hitherto supposed that the zinc employed in question the moral government of God. To this topic the these experiments is used in a pure state. Such, howDuke of Marlborough (who, without doubt, had often heard it urged in the licentious court in which he had been ever, is not the case in practice, nor is it necessary to be brought up), evidently alludes, when he says to the so. The zinc usually employed in the construction of gal- Duchess, in his letter of August 26, 1709,-"I cannot help vanic apparatus contains traces of tin, lead, and a small por-being of opinion, that, however insignificant we may be, there tion of iron. On immersing a piece of zinc in dilute acid, happiness. If anybody had told me, eight years ago, that, is a Power above that puts a period to our happiness or unthe small particles of iron and the zinc form numerous voltaic circles, their currents are transmitted through the acid, and much hydrogen gas is generated by the decom. position of the water. Pure zinc is very slowly acted on by dilute acid. If, however, common zinc have its surface amalgamated by dipping it into dilute nitric acid, and then rubbing a globule of mercury over it, by means of a cork, the zine thus prepared resists the action of dilute acid as well as the purest zinc; and the advantage gained is that the apparatus is less slowly corroded-the mine currens are not established, and thus the general results of the principal current are more effective. We have hitherto spoken of the current formed by the action of two dissimilar metals and a liquid acid, but it is not necessary that the liquid be acid; it may be alkaine-it may be neutral-or it may be pure water only; but in the last case the electric current is so feeble as not to be detected by ordinary tests. In every case, A current is said to be closed when metallic contact between the plates or conducting wires is made; and the current is said to be broken when such is not the case. after such success, and after you had been a faithful servant twenty-seven years, that ever in the queen's life-time we should be obliged to seek happiness in a retired life, I could not have believed that possible."—WARBURTON. By continual meditation in the sacred writings, a man as naturally improves and advances in holiness, as a tree thrives and flourishes in a kindly and well-watered soil. All the fruits of righteousness show themselves at their proper season as opportunity calls for them; and his words, which to the ground, but are profitable as well as ornamental. are to his actions what the leaves are to the fruit, fall not Everything in him and about him serves the purpose for which it was intended; his brethren are benefited by him, and his Maker is glorified. How eminently is this the case with that tree of life which Jehovah planted in the midst of his new paradise, by the waters of comfort; a tree which sprung out of the earth, but its height reached to heaven, and its breadth to the ends of the world! its shadow is for the protection, its fruit for the support, and its leaves for the healing of the nations. It flourishes in immortal youth, and blooms for ever in unfading beauty.-BISHOP HORNE PROPOSED ROUTE TO THE PACIFIC ACROSS THE ISTHMUS OF PANAMA. In various parts of the globe we find narrow necks of land which, by separating oceans, seas, or bays from each other, render necessary a more circuitous route for those who travel by ship from one to the other. The well-known isthmus of Suez affords a striking example of this kind. The Red Sea, which is connected with the ocean immediately contiguous to India, is so near the eastern end of the Mediterranean that if a canal or strait communicated from one to the other, the voyage to India would be shortened many thousand miles, by rendering unnecessary the circuitous route round the Cape of Good Hope. So important is this consideration, that even now the officers of the Indian army are accustomed to travel by land across the narrow isthmus which separates the two seas, and we doubt not that a canal or a railroad will one day be formed in that spot. Another instance of a similar kind, but not so well known, is the isthmus which connects North and South America, and which separates the Atlantic from the Pacific; this is the Isthmus of Panama, or of Darien. As there are, at the present time, projects on foot for establishing a route to the Pacific via this isthmus, we will briefly explain the nature of the difficulties to be overcome. On inspecting a map of America, we see that the two portions of that great continent are connected by a singular strip of land, most irregular in all its forms. It is principally comprised by a part of Mexico and the Republic of Guatemala; but, at its southern extremity, near the junction with South America, the strip of land becomes narrower than at any other part, and obtains the name of the Isthmus of Panama, or of Darien, (Parama being the name of a town on the Pacific side, and Darien that of another on the Atlantic side.) The Andes, generally speaking, stretch along the whole strip of land; but there are a few spots where such is not the case; and there is also one locality in which a lake occupies a considerable portion of the width of the isthmus. These two circumstances have led to the projects which we proceed to describe. Humboldt enters at considerable length into the subject of a passage across the isthmus, and enumerates no fewer than nine different routes, all of which might be possible for a canal: the gigantic nature of his plans, Lowever, caused them to be viewed as impracticable. By about the year 1825, the attention of merchants, both in England and in America, being turned to this salject, Captain Pitman published a volume, in which he examines the relative merits of five different routes across the isthmus. One of these was from the Gulf of Darien, close to the shore of South America, across a Barrow part of the isthmus, to the Gulf of St. Michael, in the Pacific coast; this would require a ship canal about forty miles in length, and cutting through the hills 8 stupendous as to render improbable, however possible, the prosecution of such a plan. The second route mentoned by Captain Pitman is somewhat westward of the former; the ground has fewer elevations than the former, but the ports at either end of the route were deemed so defective as to be unfit for the reception of large mert ships. The third route proposed was at a spot, use to the southern end of the isthmus, where the chain of the Andes is so completely broken as to afford a flat aluvial soil, from a river which flows into the Atlantic, to another which flows into the Pacific; it was proposed to connect these two rivers by a canal, but the rivers themselves are said to be too small and shallow to Five any but small craft. The fourth route was some sireds of miles to the north-west, where the width of the isthmus was practically lessened by the intervention of a lake. The fifth route was in the state of Mexico, at that part of the isthmus which approaches to North America; the width here, at one part, is about a hundred and fifty miles, a considerable portion of which is occupied by two rivers, which it was proposed to connect by a canal. The object of Captain Pitman was to examine the relative practicability of the several proposed routes, and to point out some of the difficulties, but not to advocate any one in particular. In November, 1827, Mr. Lloyd, an officer under Bolivar, (who was then chief of the Republic to which the Isthmus of Panama belonged,) received instructions to survey the isthmus, in order to ascertain the most eligible line of communication across it, either by road or canal, with a view to establish regular commercial intercourse from the Atlantic to the Pacific. Mr. Lloyd made a very careful examination of the height of the ground between the two seas, and also of the level of the seas themselves, both of which are obviously import ant in relation to the cutting of a canal. He found that the highest spot of ground, in that route, which was deemed the most level, was 633 feet above the Pacific. He found also that the level of the two oceans was subject to singular changes; for, in every twelve hours, and commencing with high tides, the level of the Pacific is first several feet higher than that of the Atlantic; it becomes then of the same height; at low tide it is several feet lower; again, as the tide rises, the two seas become of one height; and finally, at high tide, the Pacific is again the same number of feet above the Atlantic as at first. These variations are due to the circumstance that the rise and fall of the tide are greater on the Pacific than on the Atlantic side of the Isthmus. What effect this inequality would have on a water communication from the one ocean to the other is an important question in canal engineering. Mr. Lloyd was of opinion that a communication could be formed across the isthmus, partly by river navigation, and partly by railroad. There is on the Atlantic side a sea-port, called Chagres, and another on the Pacific side, called Panama, and the country between them is so entirely free from mountains that the greatest height is, as before mentioned, 633 feet. A river, which enters the Atlantic at Chagres, is navigable to a considerable extent into the isthmus; and Mr. Lloyd proposed to construct a harbour and other maritime conveniences near its mouth. At a certain point in the interior a station was fixed upon at which the travellers or the merchandize would leave the river, and thence be forwarded by land the remainder of the distance to Panama, a railroad being formed for that purpose. It need hardly be observed that such a project as this could not be carried out unless the government of the country were in a tolerably settled state, and considerable capital were afloat therein. How totally different from this has been the condition of these wretched republics of Central and South America, is well known to those who have paid any attention to the events of the past fifteen years. Nothing has since been done to follow out the plans of Mr. Lloyd. A few years after the mission of Mr. Lloyd, a circumstance occurred to direct attention to another part of the isthmus, which, though not so narrow as that between Chagres and Panama, has a central lake, and a river flowing from thence into the Atlantic. In the month of January, 1833, the Spanish merchants residing at Kingston, Jamaica, and connected with the commerce of Central America, requested the senior naval officer at Port Royal to allow a certain extension of the voyage made by the mail-packets in that region, with a view of establishing a communication, by commerce and corre spondence, with the towns near and around the lake here alluded to, called Lake Nicaragua. The river San Juan de Nicaragua flows from the lake into the Atlantic; and the Jamaica merchants thought that, if a monthly communication were kept up between Jamaica and the town of San Juan at the mouth of the river, a great accession | Barnett, of the ship Thunder, in a paragraph in the of commercial dealings would result. Nautical Magazine, states,― Captain Phillips, who communicated a letter to the Geographical Society of London in relation to this subject, draws a comparison between the route to the Pacific by the way of Panama, and that by way of Lake Nicaragua, and says,— The passage by Panama leads alone to the Pacific, whilst the passage by San Juan de Nicaragua would affect the whole of the internal commerce of Costa Rica and Central America, and most likely be not only the means of a commercial transit to the South Seas, but, from the influx of strangers, and the interchange of ideas naturally arising from it, would tend to enlighten this district of the country, which civil war, with all its horrors, is fast driving to the lowest stage of ignorance and barbarism. We fully join in the opinion that, if a commercial route could be established in any part of this isthmus, an amount of moral benefit might result, fully equal in extent to that which would be derived by commerce. The Lake Nicaragua, which is proposed to form part of the route last spoken of, is upwards of a hundred and twenty miles in length, and forty in breadth at its widest part, without narrowing much at either end. It is interspersed with islands, some of which are of great height. On this inland sea the Spaniards, when Central America belonged to them, kept a marine, consisting of a brig of war, of fourteen guns, and several schooners, or gunboats, so that its fitness for navigation is manifest. An English merchant had, nine years ago, a schooner of forty tons' burden, engaged in commercial enterprises on the lake. On the shores of the lake are two flourishing towns, Grenada and Nicaragua, the latter being only fourteen leagues' distance from a convenient port on the Pacific. Hence arose the idea of forming the communication by this route; for the lake can be attained through the river, which flows from it into the Atlantic, and the rest of the journey, fourteen leagues to the Pacific, would have to be traversed by road, railway, or canal, according to the nature of the ground and the views of the speculators. After it became evident to the merchants who traded in those regions that the proposed communication might be made, the points for discussion were, whether a canal or a railway would be best adapted for the portion of the route between the lake and the Pacific, and by whom and what funds the enterprise should be undertaken? If the government of the Republic could not or would not effect it, then a private company, sanctioned by the government, must do it. Both of these questions remain unsettled to this day. A few years ago, Mr. Bailey, having ascertained the possibility of constructing a railroad from the lake to the Pacific, the Columbian government granted him two thousand dollars for the purpose of making investigations respecting the other part of the route. The river San Juan flowing from the lake into the Atlantic, cannot at all times be ascended by ships, on account of rapids and shallows which interrupt some parts of its course, and Mr. Bailey was empowered to examine the river, with a view to ascertain the practicability of constructing a canal which would avoid these obstructions. But long before the completion of the investigation, the money was expended, the engineer and his assistants were disabled by sickness, and the anarchy in which the country was placed put an end to any further aid from the government. In the month of March, 1840, while H. M. S. Thunder was engaged in the survey of the eastern coast of Central America, Mr. Laurence, an assistant surveyor, with a crew of six native canoe-men, voyaged up the river San Juan, from its mouth to the lake, in a canoe. The results of that voyage, as far as regards the nature of the surrounding country, were interesting, but it was fully proved that no ship or steamboat could ascend the whole course of the river from the sea, except under extraordinary circumstances of wind and tide. Captain Mr. Bailey is said to have been employed by a company of American speculators. This, however, is not the fact, although the merchants concerned in the South Sea fishery are extremely anxious to effect a communication; but nothing will be undertaken by them unless they are convinced it can be accomplished by the way pointed out in Mr. Bailey's mission, which, by affording the means of rapid transport of the cargoes and supplies, would enable the whalers to remain entirely in the Pacific. Of course the spur which would be also given to the commerce of Central America is not lost sight of, but the anarchy, confusion, and distrust which now so ruinously degrades this disruptured Republic, throws the prospect of such desirable results to an immeasurable distance. The opinions here expressed, as to the fatal effects which national anarchy exerts in the prosecution of such an enterprise, is shared by others who have since visited the country. The Chevalier Emanuel Friedrichsthat, Indolence is there who has recently traversed the district bordering on the last sixteen years. Under such circumstances, (says M. Friedrichsthat,) the important question of a union of the two oceans has been entirely forgotten; and I believe that I do not err in asserting that Europe pays far more attention to this grand project than the inhabitants of Central America, wholly uncommerce, and with the means of promoting it. It is also acquainted as they are with the advantages of an extensive not to be expected that this state, with its limited resources, should ever be able to accomplish such a work; and it was therefore proposed, before the last war, to engage some mercantile houses of Paris in the execution of this project, the recompense consisting of tolls and fifty square acres of land. A point has been found where the Lake Nicaragua approaches within sixteen miles of the Pacific, but a hill, six hundred feet high, would have to be cut through in forming the passage; and it is evident that M. Friedrichsthat's remarks apply with full force to the commercial and financial difficulties of such a piece of engineering in the present state of the country. Not many weeks ago a meeting was held of merchants in London, connected with the South Sea trade, with a view of establishing a Joint Stock Company, for working out the plan in one or other of its forms. Opinions were stated as to the relative advantages of a railway and a canal, and the general feeling seemed to be that the project was neither a wild nor an impracticable one. A few years of tranquillity in Central America would doubtless bring about the fulfilment of this great undertaking. In all the operations of Nature there is a view to the future: which have no other aim beyond mere present gratification, it should be so with the actions of man; and those pursuits are unworthy of him.-SOUTHEY. Ix your commerce with the great, if you would have it turn to your advantage, you should endeavour, if the person be of great abilities, to make him satisfied with you; if he be of none, to make him satisfied with himself.-WARBURTON. LONDON: JOHN WILLIAM PARKER, WEST STRAND. ELBA, the Ilna or Ilva of the Etruscans and Romans, and called Æthalia by Strabo, is an island in the Mediterranean sea, near the coast of Tuscany, and separated from it by the narrow channel of Piombino. Its shape is very irregular; its length is about eighteen miles, and its greatest breadth, which is on its east side, is about ten miles; in its west part it is six miles broad, and towards the middle of its length it is only three, in consequence of the coast being indented by gulfs both from the north and south. The prevailing rocks seem to be granite, claystone, and limestone passing into marble; but near the coast, being continually triturated and battered by the winds, and by currents, and surges of a sea often tempestuous, the shores present numerous sharp angles, encroaching upon the land, or jutting out into the water, of which the number and shape vary continually. The area of the island is about 154 square miles: it is very mountainous; the highest summit, Monte della Capanna, in the west, is 3600 feet above the level of the sea. In ancient times Elba seems to have been populous. Virgil, in the Eneid, states that it contributed 300 chosen soldiers to Æneas, in his wars with Turnus. Silius Italicus states that, after the unfortunate day of Trebia, it sent (the same number with Sicily) 3000 excellent archers, armed and equipped, and a vast quantity of arms, to the Roman consuls. VOL. XX. In the year 1778, the number of inhabitants scarcely amounted to 8000: in 1808 it was nearly 12,000, and it is now estimated at about 13,500, of which Porto Ferrajo, the capital, has about 3000. Porto Ferrajo lies on the north coast of the island: it has an excellent harbour, and is strongly fortified with two citadels on the hill above it, between which is the palace formerly inhabited by Napoleon. It is a plain house, of two stories, with wings. It commands, towards the south, a fine view of the town, harbour, and mountains; and, in the north of Piombino, the coast of Italy, as far as the mountains of Lucca, and the islands to the west. Not a boat can stir without being observed. The whole of this ridge, which is a rocky promontory or peninsula, projecting into the bay, is quite destitute of foliage. The rock, the houses, the bastions, and the flanking walls of the fortifications, being all white, are distressing to the eyes; and the heat in summer would be almost insupportable, did not the sea-breeze temper and freshen the air. The town has two parish churches, one hospital, and a lazaretto. good road, five miles in length, made by Napoleon, leads from this town to Porto Longone, on the east coast, on a deep bay, where there is good anchorage for vessels. The castle of Porto Longone is on a steep hill, and is regularly fortified. The town is small, and numbers about 1000 inhabitants. The other principal towns or villages in the island are Rio, Marciana, Campo, and Capo Liveri. 639 A |