worthy of consideration. Thirdly, from be so fortunate as to obtain for the their situation beneath the surface, they inventor the notice of any competent are not liable to be impeded by floats of practical man, so that it might be ice, or by storms; therefore, I think they applied in actual steam navigation, or might be suitable to packets for despatch, if it tend when introduced to relieve and might be used all the winter. the canal proprietors from the diffiFourthly, they make no swell or commotion, either disagreeable, or dangerous, in culty into which they are likely to the water, as the common wheels do when fall, it would be found to justify the lighting in a fermentation of air and wa- favourable opinion of it now entertainter; but go as smoothly as a vessel under ed by sail their action being in the solid water Yours, truly, as a lever upon a rock for a fulcrum. G. BIRKBECK. THE JEWELRY TRADE. I shall decline saying any more at pre- Jan. 18, 1825. sent upon the principle, and leave it, sir, to your very superior judgment to comment upon. The apparatus has been shown several times to some gentlemen of the first respectability and genius, both mechanical and nautical, and has constantly met with the highest approbation. I remain, &c. 35 Deptford-Green, Į Sept. 28, 1824. S JOHN SWAN. We are informed that one of the first measures of the ensuing session of Parliament will be the regulation of a standard for all articles manufactured from gold. Such a measure as this has long been wanted, to protect the public from the unfair dealer, and also the reputation of the hoDescription of the Engraving. nest jeweller from the suspicion On the axis E. fig. 1, supported by the which attaches to the trade but too frame work, F, G, are placed the vanes, A, generally. It is, indeed, almost inB, and C, D, having a surface equal to credible, that whilst the Legislature that of the floats of the paddle wheels, should have fixed the standard of which are immersed whilst acting: these plate, and of certain articles, such as are so situated with respect to each other, watch cases, &c. it should have left that whilst working they act as a screw no other barrier to imposition in the within the water, and thus draw the ves- more numerous and expensive artisel forward.. The angle which these planes make with their axis is about 30°. At H is seen the end of the crank, on cles of jewelry, than the conscience of the manufacturer. At present, no which the wheel I is fixed to convey the man who purchases a gold seal or a motion of the engine through the train K, has the slightest satisfaction on the chain, or any small article of jewelry H, I. This machinery, however, is merely a suggestion; and probably a better score of its intrinsic value; whereas, and more simple mode might be devised in other countries, the smallest artifor producing the requisite motion. The cle is stamped by a government officonvenient manner in which this plan cer. In France, for instance, when adapts itself to the vessel is observable in the end view, fig. 2, where it may be seen to lie entirely beneath that part of the deck which extends from A, to B. The dotted lines represent the axes within the vessel, on which the wheels, I, I, fig. 1, belonging to each side are fixed; and F, in the same figure, shows the crank on one side. G and H represent strong bolts, by which the whole apparatus is attached to the vessel, affording a very ready method of disengaging them, whenever circumstances may require such separation. If by this description of what seems to be an excellent contrivance I should. a person purchases a new article of jewelry, he can throw his old gold into the scale of the jeweller, and insist upon his weighing it against Napoleons, the sterling coin of the country, and allowing its full value. When the purchase of a gold chain is made in Paris, its weight is charged first, and the fashion afterwards, So that its intrinsic value may be fairly ascertained. So just a mode of protecting the public cannot be too warmly praised, or the example too speedily be followed. Mechanics' Register. SELF-REGISTERING THERMOMETER, f A Description. A represents the Thermometer." B, its fulcrum, or point of suspension. C, pinion work to increase the motion of the index. D, main index. EE, registering indices. G, level to adjust the instrument. Those at present in use, the result of a pretty thorough investigation of the subject, are as perfect, perhaps, as human skill and art will allow; but as adding to the variety of modes by which similar ends may be obtained, the foregoing is proposed for the consideration of the curious. The large bulb and tube of this thermometer are to be filled with mercury, so that when suspended on its fulcrum the expansion and contraction of the metal shall altogether take place in the small bulb, which is shown without the scale in the above diagram. Some attention will be necessary in graduating it, particularly on account of its form and dependant movements; but as the expansion and contraction is only sensible at one point, if the apparatus be large, it will indicate the changes of temperature with at least as great accuracy as those in which a liquid constitutes the index, by moving through the variable calibre of glass tubes, more pecially as such for registering purposes require to be of comparatively large dimensions. es The freezing and boiling points may be obtained by placing the Thermometer scale and all in water of the requisite temperature. These ascertained, and the fulcrum moving easily on the rests of the fork, it is evident that the gravitating centre of the Thermometer will constantly and regularly change its position with the change of temperature in the surrounding media, and cause the bulbs to describe arcs of a greater or less number of degrees, according to the increment or decrement of temperature, the relative weights of the two bulbs, and their proximities to the fulcrum. The apparatus constructed with a single index, will answer all the purposes of a common thermometer, and if two others. furnished with small stops or pins, be added, so as to be operated on by it, in both its moving directions, they will indicate the greatest daily or other periodical changes of temperature, provided they be set for the purpose. Allow ance, however, must be made for the inconsiderable resistance of their motion, which may at any time be measured by noticing where the main index rests, when free, and how much it falls short of that point when obstructed by the resistance of the registering indices. This Thermometer will require to be adjusted by an appendant level, or by turning the scale so as to make it correspond with another thermometer, known to agree with it. The freezing point should be adjusted very little below a horizontal line passing through the fulcrum. Barometers may also be constructed to operate on the same principle that governs the movements of the before described Thermometer. Both the above instruments may be made very minute and accurate measures for determining the elevation of mountains, hills, or any less height; for their structure admits of the use of any quantity of mercury that may be necessary to obtain a clock-work movement, that shall in dicate the difference in altitude of a single foot. The resistance of friction may be accurately ascertained, and the operations of the instrument so insulated, and the calculations so simplified, that almost any individual possessed of vision may use it. By those now in use, approximations to facts can only be expected, because of the convexity of the mercury in the tubes, and the great nicety that their management requires; besides, they are exceedingly liable to be broken or injured, which need not be the case with those above, for the tube may be made of iron, which, while travelling, should be detached from the clock work apparatus. STEAM GUNS. French government. We now find We stated, in a former Number, that the French had laid claim to the merit due to Mr. Perkins's invention for firing balls by steam; and explained, at the time, the difference which really existed between his invention, and that which was submitted to the TO CLEAN PICTURES, &c. floating batteries which nothing can resist. We will imagine a fleet of steam boats sailing for the English coast, profiting by a calm, when the wooden walls of old England cannot act, or proceeding with enormous speed boldly by our vessels, into which they throw tons upon tons of water, deluging the decks, and preventing the men on board from working the guns; then attacking open and defenceless towns with shells or cannon, and turning back with impunity. Now there is nothing visionary in all this-it is perfectly practicable, and will be practised-the French are preparing for it even now! With honied words of peace in their mouths, they have war in their hearts, and are silently laying a train which may explode with an effect the more violent, as it was the less expected. Let it not be said again, as it has been long foolishly said, that the French will be years and years before they can attain sufficient mechanical power for all this; whereas, England, in a few weeks, could do all that is necessary. Is there not at this moment in Paris alone, a steam engine manufactory, with 250 men (all Frenchmen except two, the active partner and the foreman) in full activity? And has not this manufactory alone, in less than two years, turned out upwards of 400 steam engines? Let us hear no more, therefore, of the inability of the French nation to put into execution their project of steam war vessels; but, like a wise nation, prepare for them at once, by devoting all our energies to a preparation which would avert war. If the French find us so preparing, they will be careful how they begin; but if we sleep at our post, we shall wake one day in alarm, and find that the frog-eaters are not so contemptible as we conceived them to be. Mechanics' Register. TO CLEAN PICTURES. 263 nous bodies and foulnesses; such as sugar, honey, glue, and many others; and it will also take off any varnish of gum Arabie, glair of eggs, or isinglass, and is therefore the greatest instrument in this work. It may be used without any caution with respect to the colours, as it will not in the least affect the oil which holds them together. Olive oil, or butter, though not generally applied to this purpose, will remove many of those spots which resist even soap, as they will dissolve or corrode pitch, rosin, and similar bodies, they may be used very freely, having no bad effect on the painting. Pearl ashes, melted in water, make a proper dissolvant for most kinds of matters which foul paintings, but this must be used with great caution.Spirit of wine, as it will dissolve all the bic) is very necessary for taking off picgums, and gum rosins, (except gum Arature varnishes composed of such substances; but it corrodes the oil of paintings, and softens them in such a manner as to render all rubbing dangerous while they are under its influence. Oil of turpentine will likewise dissolve some of the gums used for varnish; but spirits of wine will generally answer the purpose much better. When paintings appear to have been varnished with those substances that will not dissolve in water, they are very easily and safely removed by the following method, viz. Place your picture, or painting, in a ther flood the surface of it with strong rechorizontal position, and moisten, or ratified spirits of wine; but all rubbing, beyond what is absolutely necessary, must be avoided. Keep the painting moist, by adding fresh spirit, if requisite, for some minutes, then flood the surface copiously with cold water, with which the spirit, and such part of the varnish as it has dissolved, may be washed off; but in this state of it, all friction must be avoided.When the painting is dry, the operation may be repeated, until the whole varnish is removed. Mechanics' Register. PREPARATION OF GINGER BEER Take two drachms of fine loaf sugar, eight grains of ginger, and 26 grains of carbonate of potash (all in fine powder;) mix them intimately in a Wedgewood's ware mortar. Take also 27 grains of ci 264 PRESSURE AND RAREFACTION OF THE AIR, &c. tric or tartaric acid (the first is the pleasantest, but the last the cheapest.) The acid is to be kept separate from the mixture. The Beer is prepared from the powders thus:-Take two tumbler glasses, each half filled with water; stir up the compound powder in one of them, and the acid powder in the other; then mix the two liquors. An effervescence takes place the beer is prepared, and may be drank off. It must be drank off directly, or it will become flat. is the safety of life and property, in cases of fire, or where any suffocating or noxious vapour exists. It consists of a hood. and mouth-piece, so contrived as to render the wearer enabled to breathe with perfect ease and safety in the midst of the densest smoke. In case of dwelling houses, warehouses, factories, ships at sea, &c. being on fire, its advantages are incalculable. Roberts exhibited the efficacy of the above extraordinary discovery at the mines of the Earl of Balcarras, a few weeks since, to the complete satisfaction On Wenes PRESSURE AND RAREFACTION OF of those who witnessed it. THE AIR. The pressure of the air, and its rarefaction by heat, are excellently illustrated by the following simple experiment:-Take hold of a wine glass with your right hand, and with your left put into it a small piece of burning paper. When the paper has burned for a few seconds, strike the mouth of the glass against the palm of your left hand, and it will remain firmly fixed to it for a considerable time. The cause of this is, that the internal air is so rarefied by the burning paper, that the pressure upon the inside of the glass is greatly diminished. The equilibrium, therefore, of the pressures upon the outside and inside of the glass being destroyed, the glass must adhere to the hand till that equilibrium is restored. SINGULAR OPTICAL DECEPTION. When the wheel of a carriage in motion is attentively viewed through vertical bars, such as the rails of a pallisade, or the laths of a Venetian blind, the spokes appear to bend downwards, and more or less so as they are situated farther from or nearer to the spoke which happens to be vertical, and which always appears to be perfectly straight. Dr. Mark Roget, in a paper which he has addressed on the subject to the Royal Society, explains this curious phenomenon by supposing that. the impression made on the retina by a pencil of rays, when sufficiently vivid, continues for some time after the cause has ceased. He thinks it even possible to estimate the actual duration of any impression on that organ, from the apparent velocity of the spokes. IMPORTANT INVENTION. A person of the name of Roberts, who is at present in Bolton, has constructed an apparatus which will prove useful and valuable in the highest degree. Its object day week, at the recommendation of several persons in Bolton and the neighbourhood, of the highest respectability, he invited some of the principal tradesmen and inhabitants of the town to meet him at Messrs. Crook and Dean's Foundry, Little Bolton; where he demonstrated the infallibility of his apparatus, to the utter astonishment of a very respectable party of gentlemen. In the course of the trial, he went into a stove room, in which sulphur, hay, &c. were burning at the same time. He was shut in for the space of 20 minutes, and came out at the expiration of that time perfectly sound and uninjured. Had any one, without the apparatus, remained in the room longer than a minute, it would have been attended with certain death. The invention will be submitted to the Society for the encouragement of Arts and Sciences. He has been advised by some to apply for a patent; but like all who are possessed of true genius, he is modest and unobtrusive: and consequently abhors quackery, or even the appearance of it. He prefers allowing the public the full benefit of his exertions, and trusting to their benevolence, as the reward of his labours. We understand that some gentlemen are endeavouring to raise a subscription for him. Mr. Paixham (a Frenchman) has invented a mortar which throws bombs ho rizontally, exactly in the same manner that cannon discharge balls. This bomb cannon, executed under the orders of the Marquis de Clermont Tonnerre, was lately proved at Brest. It answered every expectation, and carried as far as the largest ship guns. The bomb went true to the direction, and the effect produced was so powerful, that considerable changes are immediately to be made in the naval materiel. In consequence of this new inven |