Schools of Practical Mechanics. HE intelli gence and been mastership of many-and, we may truly add, is also incapable of adding to the resources of his own profession by a comparison with others. It is only necessary to observe the number of trades and professions which radiate, as it were, from one particular operation, and to bear in mind, the step by step progress which almost every manufactured article, from a pin to a pistol, or a tea-kettle to a steam-engine has to make ere it is finally disposed of, to be at once impressed with the conviction that universal knowledge ought to be the great desideratum of the age-a knowledge that would tend more to open the eyes, hearts, and minds of men, than any project that has been set on foot since the world began. But how is this to be obtained? inquires the reader. We answer, let him look at the various schools of design now dispersed about the country-let him review in his own mind the vast amount of good these have been the means of effecting, and then ask of himself whether the principle cannot be extended in its application? Whether, in fact, schools could not be established to teach the mechanic the true practice of his own and its analogous professions? The schools of design are superintended by masters of ability-the schools we propose could also be superintended in a like manner. At all events, we are certain that the principle, if adopted by government, would be as much to the national advantage as it most assuredly would be to its credit. the English mechanic have ever THE "PERIL INDICATOR."-There is now in celebrated by historians and contempora-peril indicator," to denote the approach of Portsmouth dockyard a working model of a neous writers; and, in our own age, we have had good practical evidence of the ground to ships and steamers, the invention of genius which too often lies neglected Lieutenant Westbrook, R.N. (1826), of the within the brain of the working-man-only Stag revenue cruiser, on the Ryde district. requiring education to loosen it from its bond-The apparatus is positively too simple to deage, and to bring its resources to bear on the scribe: it is fitted to the keel of the vessel, improvement of our arts and manufactures. and consists of a projection therefrom of two Of late years, the establishment of mechanics' bars, ten feet below the keel of the vessel; iminstitutions in various parts of the country, and mediately these bars, which are fitted forward more particularly in the metropolis, has, doubt- as well as aft, touch ground, they spring up less, effected much in the right direction; but level with the keel and ring a large bell in the these, too often, from their limited resources, engine-room, which is the signal for the enalthough invaluable as places where the work-gineer to instantly reverse the engines and ing-man may obtain really sound miscellaneous send the ship astern. The invention has met knowledge, are inadequate to the purpose of with the approval of some of the members of leading him, by means of a systematic course of study, through the broad field of mechanical science, and of implanting in his mind not merely rudimental but practical knowledge of processes and their results-of causes and their effects. It has been justly observed that NEW MOTIVE POWER.-On the 20th of last the man who is merely acquainted with but one month, M. Lafond took out a patent for the department of art or science is incapable of application of chloroform, as a motive power in appreciating the enjoyments arising from a place of steam. the Admiralty, and every scientific naval or other person who has seen it. A trial would fully demonstrate its usefulness and applicabilty; its expense is too trivial to be an obstacle. Royal Academy. lesser and younger figure, with a crescent on her brow, and with white drapery, half encircled her with one arm, while she extended the other towards the sun, with an urn also. Mercury, Venus, Mars, &c., all revolved in their proper PROFESSOR LESLIE'S SECOND LEC- places; and the entire composition TURE ON PAINTING. managed with great skill and taste. was After adverting to the rage for Grecian cosTHE learned professor commenced his second tume which was prevalent some years back, lecture to the students of the Academy and which he happily denominated the "Greek by remarking that he was about to give mania," the professor stated that he was not several examples of the powers of inven-insensible to the sincerity of expression, the tion and expression, taken from different grace, and the happy inventions that chracterschools and from different walks of art, and ised the works of the early Italian masters, or he observed that he had adopted this course the many exquisite traits of Nature by which because the method of classifying the various their immature art was adorned. They were branches of art, according to difference of the worthy precursors of Michael Angelo and style or subject, had never in his opinion been Raffaelle; but he could not agree with a recent successfully carried out. critic, who stated that Michael Angelo's picture of the "Last Judgment" stood far below the dignified grandeur of Orcagna in the_treatment of the same subject in the Campo Santa, at Pisa. That Michael Angelo borrowed his figure of Christ from the latter, he (the professor) would admit; but he thought that if Angelo had trusted to his own judgment and invention, he would have succeeded better. Originality in painting depended entirely on the painter's powers of observation, and it constituted the difference between the greater or lesser artist, that the one was thinking of art at all times, while the latter only reflected upon it in the studio. Too much time could never be devoted by a painter to filling his sketch-book with whatever interesting objects he happened to come across-they were always of utility. The professor then remarked upon the degree of fame which had been gathered both by The professor remarked that the importance Raffaelle and Michael Angelo, and, after critiof the constant observation of Nature to the cally examining the grounds which these painter of real life would be readily admitted, artists founded their reputation, stated that the but such habits were of no less value to the former had painted the least number of picpainter of the most imaginative class of sub-tures, with the exception of one (Leonarda di jects. The supernatural was not the unnatural; Vinci), of any man, and the latter, taking his -the centaur, the sphynx, the satyr, &c., were early demise into account, comparatively the but combinations of Nature, and there was most. true taste exhibited in making these ideal He then entered into some remarks upon beings act naturally an example of which Hogarth-a master who was wholly unequalled might be taken from the Phygalian marbles, in invention and expression, excepting by Rawhere a centaur was made to bite his antago-ffaëlle alone. No painter whatever, and but nist, &c. Ghosts and witches required some considerable degree of attention in their treatment by the painter-materiality should be avoided as much as possible, and the imagination taxed to concoct that well which it is impossible to bring before the eye. In this department of painting the great Fuseli stood pre-eminent, and yet he never painted anything that might seem unnatural to the most scrupulous critic; while Sir Thomas Lawrence, in his picture of "Satan," gave so much materialism to the form of the evil one as to be utterly unnatural with reference to the subject. few writers, had laid bare the evil dispositions of human nature, and their inevitable conse quences, with such a mastery of illustration. Hogarth was a painter of nature in the highest sense, as distinguished from a painter of matter-of-fact. He failed, however, in religious subjects, although there were touches in his pictures taken from scripture subjects which distinguished them from the productions of commonplace minds. Hogarth, it was true, was often gross, but the age in which he lived was much less fastidious than ours, and his great object was to expose vice in all its deformity. Debauchery he always made detestSymbols, personification, and allegory next able-never attractive. He was not-it was. came under notice, and the professor re- to be owned-a ladies' painter,-for ladies, marked upon a beautiful instance by the late fortunately for themselves, knew nothing of president (Mr. Howard) of graceful personifi- the life which he chiefly satirised. But it cation which adorned a ceiling in the princely was no sign of a healthy masculine taste to mansion of the Duke of Sutherland. It was a object to what Charles Lamb denominated his circular composition in which he (Mr. Howard) | " had most successfully availed himself of the mythologic names of the sun and the planets. Apollo sat in the centre, and the composition was so contrived that the earth, represented by a graceful figure of a female attired in a green mantle, was nearest to the eye. Her head was crowned with towers, and she seemed to do reverence to the god as she passed him, holding forward an urn to receive his rays. A strong meat for men." GUTTA PERCHA MEDALS.-We have lately inspected some specimens of castings in gutta percha; but we consider that it is not entirely suitable for the purpose: the outlines are generally badly preserved, and the whole in many cases indistinct. Gold and Gold-Beating. coining was invented, it passed for money in the condition in which it was found in the earth; and in this form it still enjoys a currency in many parts of Africa. It is rarely employed in a state of perfect purity, but is almost universally alloyed with copper, or with silver, in order to increase its hardness. The alloy of gold and silver is found already formed in nature, and is that most generally known. It is distinguishable from that of copper, by possessing a paler yellow than pure gold, while the copper alloy has a colour bordering upon reddish yellow. A variety of means are employed to judge of the quality of alloys, supposed to consist in part, or principally, of gold, without resorting to a regular analysis. GOLD is the most precious metal employed in commerce. It is exceedingly soft and flexible, but its tenacity is sufficiently great to sustain, in a wire one-tenth of an inch in diameter, 500 lbs. weight without breaking. In hardness it is superior to lead and tin, but inferior to iron, copper, plantinum, and silver. Its lustre does not equal that of steel, platinum, or silver, but it surpasses the other metals in this respect. It may be exposed for any length of time to the atmosphere, without suffering the least change. It is also unalterable in the common fire; but on being exposed to power- The art of gilding metals (see p. 52, vol. ii.) ful burning mirrors, or to the heat of the oxy-depends upon the double property which hydrogen blow-pipe, it not only melts, but mercury possesses, of amalgamating with gold, even rises in vapour. and of becoming volatile by heat, and thus quitting the gold, which adheres strongly to has been spread. The composition of the the metal upon which the mercurial amalgam amalgam generally used is eight parts of mercury to one of gold. The malleability and extreme divisibility of gold are the foundation of the art of gold beating; and these two properties are so remarkable in this art, that natural philosophers are in the habit of quoting the results it furnishes, as examples of the divisibility of matter. Boyle has observed that a grain of gold, reduced to leaves, will cover a surface of 50 square inches; that each one of these square inches may be divided into 46,656 other little squares, and that, of course, the entire amount of surface derived from one grain of gold is capable of being divided into 2,322,800 parts, each of which is visible to the naked eye. Gold is not readily oxidised or dissolved by any of the pure acids. Its best solvents are chlorine and nitro-muriatic acid; and, according to Sir Humphrey Davy, the chlorine is the agent in both cases, since the nitromuriatic acid does not dissolve gold, except when it gives rise to the formation of chlorine. It is to be inferred, therefore, that the chlorine unites directly with the gold and that the compound formed is a chloride of gold. There is no inconvenience, however, in regarding it as a muriate, since re-agents act upon it as if it were such. The gold is precipitated from its solvent by a great number of substances. Lime and magnesia precipitate it in the form of a yellowish powder. Alkalies exhibit the same appearance; but an excess of alkali redissolves the precipitate. The precipitate of gold obtained by a fixed alkali appears to be a true oxide, and is soluble in the sulphuric, nitric, and muriatic acids; from which, however, it separates by standing. Gallic acid precipitates gold of a reddish, colour, and very soluble in nitric acid, to which it communicates a fixed blue colour. Ammonia precipitates a fine solution of gold much more readily than the alkalies. This precipitate, which is of a brown, yellow, or orange colour, possesses the property of detonating with a very considerable noise, when greatly heated. It is known by the name of fulminating gold. In consequence of the wonderful extension which the gold-beater is enabled to give to this precious metal, it is employed for ornamental purposes to an extent which, from its comparative scarcity, would otherwise be impossible. Thus it is estimated that an equestrian statue, of the natural size, may be coated with a piece of gold not exceeding ten shillings and sixpence in value. The gilding of the dome of the Hôtel des Invalids, at Paris, cost, about £5,000, and in India, where it is common to gild towers, bridges, gates, and colossal idols, it is known to be attended with still less expense. Most metallic substances precipitate gold from its solution in nitro-muriatic acid. The following is a short account of the Lead, iron, and silver precipitate it of a deep ingenious art of gold-beating. The gold used is and dull purple colour; copper and iron throw as pure as possible, and the operation is comit down in its metallic state. A plate of tin, menced with masses weighing about two ounces. immersed in a solution of gold, affords a pur-These are beaten into plates six or eight inches ple powder, called the purple powder of Cassius, long, by three-quarters of an inch wide. which is used to paint in enamel. Ether, They are then passed between steel rollers, naphtha, and essential oils take gold from its till they become long ribands, as thin as paper. solvent, and form liquors, which have been Each one of these is now cut into 150 pieces, called potable gold. The gold which is pre- each of which is forged on an anvil, until it is cipitated on the evaporation of these fluids, or about an inch square, after which they are well by the addition of sulphate of iron to the solu- annealed. Each of the squares in this state tion of gold, is of the utmost purity. The prin- weighs 6 4-10 grains, and in thickness is equal cipal use of gold, as is well known, is in coin- to 1-766th of an inch. The 150 plates of gold age. It has been with mankind, from time thus produced from one mass are interlaid immemorial, the representative sign of every with pieces of very fine vellum, about four species of property. Even before the art of inches square, and about twenty vellum leaves are placed on the outsides; the whole is then put into a case of parchment, over which is drawn another similiar case, so that the packet is kept close and tight on all sides. It Civil Engineering. is now laid on a smooth block of marble, or Ir there is one profession more than another metal, of great weight, and the workman which can be considered the favourite profes begins the beating with a round-faced hammer, sion of the day, it is civil engineering, and weighing sixteen pounds; the packet is turned, perhaps, more from its comparative nove occasionally, upside down, and beaten with to the public than any other cause. Nore strong but not acute strokes; till the gold is though it may be in its present standing, the extended nearly to an equality with the vellum practice of a civil engineer, in its various de leaves. The packet is then taken to pieces, partments, boasts of great antiquity. The and each leaf of gold is divided into four with Egyptians seem to have had a distinct corps. a steel knife. The 600 pieces thus produced similar to the French Ponts et Chaussées, or are interlaid with pieces of animal membrane, the Dutch Waterstaat, charged with the care from the intestines of the ox, of the same di- of the canals and irrigation. Hydraulic emension and in the same manner as the vellum.gineering also attained a great height of proThe beating is continued, but with a lighter ficiency among the Persians, and was doubthammer, which weighs about twelve pounds, less cultivated as a distinct art. Many of the until the gold is brought to the same dimensions engineering operations of the Persians were, as the interposed membrane. It is now again however, conducted by the Phoenicians, who divided into four, by means of a piece of cane, were evidently well practised. In cutting the cut to an edge, the leaves being by this time canal of Mount Athos, during Xerxes' invaso light that any accidental moisture, con- sion of Greece, the Phoenicians were the first densing on an iron blade, would cause them to show the proper way of executing the work, to adhere to it. The 2,400 leaves hence resulting are parted into three packets, with interposed membrane as before, and beaten with the finishing or gold hammer, weighing about ten pounds, until they acquire an extent equal to the former. The packets are now taken to pieces, and the gold leaves, by means of a cane instrument and the breath, are laid flat on a cushion of leather, and cut, one by one, to even square, by a cane frame; they are lastly laid in books of twenty-five leaves each, the paper of which is previously smoothed, and rubbed with red bole, to prevent them from adhering. an Gold wire, as it is called, is, in fact, only silver wire gilt, and is prepared in the following manner. A solid cylinder of fine silver, weighing about 20lbs., is covered with thick leaves of gold, which are made to adhere inseparably to it by means of the burnisher: successive layers are thus applied, until the quantity of gold amounts to 100 grains for every pound troy of silver. This gilt silver rod is then drawn successively through holes made in a strong steel plate, until it is reduced to the size of a thick quill, care being taken to anneal it accurately after each operation. The succeeding process is similar to the former, except that a mixed metal, somewhat softer than steel, is employed for the drawing plates, in order to prevent the gilding from being stripped off; and no farther annealing is requisite after it is brought to be as slender as a crow-quill. When the wire is drawn as thin as is necessary, it is wound on a hollow copper bobbin, and carefully annealed by a very gentle heat: finally, it is passed through a flatting-mill, and the process is complete. According to Dr. Halley, six feet in length of the finest gilt-wire, before flatting, will counterpoise no more than a grain; and as the gold is not quite 1-57th of the whole, a single grain of gold, thus extended, will be 345.6 feet long, and only the millionth part of an inch in thickness. by making the banks of their portion with a slope; while, as Herodotus relates, the other nations dug them upright, and they conse quently fell in. The Greeks, from the nature of their country and from political causes, had little call for engineering science; their mining works were chiefly superficial, and their military operations and sieges afforded little scope for great exertions. The Rhodians acted as their military engineers, and enjoyed considerable fame. Mechanical engineering also had not any great call for display among the Greeks, whose machinery either for mining or hydraulic purposes was not on a large scale. The Romans were the great engineering" people of antiquity, and have left us many noble monuments: their roads, tunnels, sewers, canals, embankments, aqueducts, bridges, and moles, were executed with great skill and foresight, and are of such durability as to have resisted the injuries of time and the ravages of barbarians. Thus, although the Roman power is annihilated, and their nation ceases to exist, they have left an invaluable legacy to Europe in their works and the profitable examples they afford. Had the literature of antiquity perished, these noble relics would still have contributed to the maintenance of civilisation and its restoration. How the architects and engineers of the middle ages profited by these studies is well known to the antiquary. Even in this country the roads, bridges, canals, and embankments left by them were well copied. The monks of the marshlands copied the Fossdyke and other Roman precedents in their drainage of the fens, and they showed themselves apt scholars in many other works. Neither were the mining-works of the Romans conducted with less enterprise and less skill. Their joint-stock undertakings for working the Spanish silver mines would have been distinguished in modern days, both on account of the extent of their workings and of their power of drainage by the Egyptian spiral. Their melting furnaces were also of respect |