auction-by their original proprietors. Perhaps Mr. Thorold could favour us with some authentic information on this point, having all the advantages of a residence on the spot?

Espy's Theory of Thunder Anticipated.-Sir,Your correspondent, who, in your number 854, P. 208, has detected the want of novelty in Espy's New Theory of Rain," might have said the same thing of Espy's equally new theory of thunder; since both these theories had been given together as parts of one scheme almost eleven years ago by Mr. Meikle, in the before cited Quarterly Journal of Science, for April, 1829; and both have also been published in the Hygrometry of the Encyclopedia Britannica-FULMEN. Glasgow, Feb. 7, 1840.

Convert ng Stone into Marble.-A discovery is said to have been recently made in Russia, of a method whereby the softest stones may be hardened, and have communicated to them the beauty, solidity, and even colours, of the rarest marbles.Athenæum.

Printing Paintings.-The Berlin Correspondent of the Athenæum adverted lately to the discovery of Herr Liepmann by which an unlimited number of fac-similes of ancient pictures can be produced at a very trifling price. I have since heard of a M. Krewel, a painter at Bonn, who is said to have been engaged for many years in making experiments on Lithochromy, or stone painting, by means of which copies of original oil paintings have been produced by the customary mode of impression. This discovery is described as particularly calculated for copying pictures of the old German school, and M. Krewel has found it to succeed remarkably in portraits. Several of these lithochromic pictures have already appeared-I have been particularly struck with one-The Saint John, known already by Muller's copper-plate engraving. The impression is taken on linen, and has absolutely the appearance of a painting. The drapery, both in colour and folds, leaves nothing to be desired."

The Arts applied to Manufactures.-Let us fancy that, some thousand years ago, a mortal, wandering through an oriental wood, saw a worm falling from a fruit-bearing tree-that he found this little creature had reached the end of one of its stages of existence, and was laboriously engaged in shrouding itself in an unknown substance, like a fine thread of gold, out of which it constructed its tomb; that, attracted by the circumstance, he found this shroud to consist of a thread hundreds of yards long, which a very little attention enabled him to detach; he found he could strengthen the threads by uniting them together, and they could be applied to various purposes of usefulness; he thought of winding off the thread; the reel lends him the first assistance, but he could not make the reel without the co-operation of a knife, or some such instrument with a sharp edge. Thus the aid of art-of the produce of art, is already called in. With this rude Instrument he makes a machine as rude, which reels off the thread coffin of the curious animal. In process of time, he finds that this fine filament can be applied to the making of garments-garments alike useful and ornamental. Now trace the progress of things by which, from the narrow sphere of his observation and experiment, his success spreads through the districts he inhabits, and from them to other lands, and becomes an object of importance to communicate with the whole family of man. By and by the cocoon, or the produce of the cocoon, finds its way to foreign countries, probably more intelligent than his own, again to be operated on by a higher intelligence and more practised skill. This associates the thread of the silk-worm with a ship, with ship-building, and all its marvellous combina. tions. Some wandering merchant probably conveyed the raw material to Persia; some adventurous

mariner to Greece or Italy, or other regions where the raw material gave a new impulse to science and to thought. But consider for a moment, before the ship was launched upon the water, how many elements were necessary for its production; think of how multitudinous and how various the materials which that ship required for its construction, before the products of that remote country are brought to their ultimate markets for manufacture. I refer to this particular topic because it is associated with the prosperity of the districts in which we are, and I wished to carry back your thoughts to the germ whence that prosperity sprung.-Bowring's Lecture at the Poplar Institution

Bursting of Steam Boilers.-Mr. Murray, in a lecture at the Mechanics' Institution, Birmingham, stated that the fearfully fatal cases of the Earl Grey steamer at Greenock, and the Union at Hull, had directed his particular attention to the enquiry as to the causes of these deplorable events. He differed entirely from the diversified solutions of the problem that had been given to the public; and ventured to state his individual opinion, as deduced from experiments, merely that it might be the means of affording some useful hints on a subject so deeply interesting and important to the community. Safety valves, he observed, (as they were called,) were merely a misnomer, and in the sudden extrication of a volume of highly elastic steam could be of little avail, while they afforded no adequate relief. There should, he believed, be always to safety valves. He mentioned a case where one of the valves of a boiler thus supplied acted freely, and the other was gagged. The latter phenomenon he did not think depended entirely on the ordinary pressure of the atmosphere, but had to do with some other principle; in proof of this, he cited the instance of a transatlantic steamer, where the safety valve was gagged, requiring the purchase of a crow bar to raise it, after the entire weights had been previously removed. Mr. Murray also considered that safety valves were much too contracted in their dimensions, and two safety valves would provide against the contingency referred to. The bursting of steam boilers was considered attributable to the sudden disengagement of highly elastic vapour or steam from the individual spot of the boiler against which a burst of flame might impinge; this might detach a portion of the calcareous incrustation at the bottom, and this extricated steam would dart like an arrow through the water, and strike that portion of the dome of the boiler immediately opposed. comparatively non-conduction, or slow conductibility of the water, would not allow the suddenly evolved vapour to diffuse or expand, and thus press equally on the vault of the boiler: the safety valve in such an emergency would be useless, and he contended that the appearance of the roofs of the boilers thus destroyed entirely corroborated these views. In proof of his assertions, Mr. Murray referred to the varied temperatures that might be observed in a vessel of hot water; there was one temperature at the top, another in the centre, and another at the bottom, while there were others in various directions laterally. This was particularly remarkable when a piece of ice was dropped into a tumbler of water. Various substances modify ebullition, such as a chip of wood in the case of ether, and might suggest important and useful hints. In a glass vessel of water, where the flame impinged, the ebullition was consequently per saltum, and unequal; while a few metallic filings served the purpose of facilitating an equal diffusion and extrication of vapour. Mr. Murray considered that the prevention of these accidents was as obvious as the application was easy-namely, the diffusion through the water in the steam boiler of copper wire-Midland Counties Herald.

The

CURTIS'S PATENT HYDROSTATIC AND SCREW JACKS.

Sir, Frequent occasion exists in the working of railways to move the ponderous engine from one line of rails to another, to lift it on to, or off from the line, or to elevate it for the purpose of getting at the under parts for the purposes of repairs. These operations have hitherto usually been effected by means of the common jack, assisted by ropes and pullies, but great inconvenience and danger has attended the operations with these machines, the slightest movement of the engine on one side or the other, after it had been elevated, causing it frequently to capsize, and several accidents, some attended with fatal results, have been the consequence. Further, when a train or engine by any accident gets off the line of rails at a distance from a station, great delay is occasioned in getting the necessary apparatus from the station, and when it is procured in effecting the replacement of the engines and carriages, as well from the greatness of the weight as from the inconvenience of the situation. I have invented and patented two portable machines which have been found most useful to railway engineers, viz, the Hydrostatic Jack, and the Screw Jack, the following descriptions of which, extracted from my specification, I beg to hand you, and shall be much obliged by their publication in your Magazine.

Hydrostatic Jack.

This apparatus consists of a machine to place or replace an engine or carriage upon the rail, and is an adaptation of the hydraulic press for the purpose of a lifting jack.

Figure 1 is a side view, one half is shown in section. Figure 3 a plan partly shown in section, and Figure 2 an end view partly shown in section; similar letters refer to similar parts of the machine in each figure, and the description refers to each figure so far as the parts are shown in each. A is the end rail of the framing of an engine or carriage which may be required to be placed upon the rails. B, two cylinders or tubes of wrought iron or other metal, furnished with stuffing boxes and leathers in the manner usually employed in hydraulic presses; rams or pistons C, C, work in these tubes in the usual way,

and the upper ends of the rams are pro-vided with notched ends or otherwise as may be found convenient. E is a force pump fixed horizontally upon the plank L; e is a metal block in which the channels are formed for the channels, valves, and adjusting screws, the general arrangement of which valves and screws is the same as in the hydraulic press, but I form it in this manner, in order to avoid the use of connecting pipes and the usual fittings, which would be very liable to be broken or deranged. F is the plunger of the force pump E, worked by the bellcrank lever G. H, a cistern to hold water to supply the pump, which is introduced into the pump through the lying valve, which is kept in its place by a spring in the usual manner; when the pump is set to work, the water lifts the vertical valves d, d, and passing through channels clearly shown in figures 1 and 2 in section, enters the cylinders or tubes B, B, and thus raises the rams or pistons C, C; the water may be prevented entering either of the cylinders, as may be desired, by screwing down the screws s, s, over either of the vertical valves, when the entire force of the pump will then pass by the free valve and enter the cylinder to which it belongs. This adjustment may be necessary to keep the engine or carriage level, and the same adjustment may be made by stopping the pump, and letting out the water from the waste holes p, p, by screwing back either of the adjusting screws o, o; the two barrels B, B, are fixed upon a strong plank, about four feet asunder, and the basement plate connecting them together is formed of a wrought iron plate rolled with a rib down the middle; this rib is bored to the requisite distance from each end, and thus the channel is formed for the water from the pump to the cylinders; the cylinders are formed with flange ends, and the joints made with the basement plate in the usual way, either with a rust joint, or lead, or other jointing; the upper plank L slides upon the long plank M, which is laid across the rails, and the projecting end supported with blocks of timber, or in any other readyand convenient manner; the plank M has fixed down the centre, the notched plate n, the centre of which sinks about an inch and half below the surface, thus forming a longitudinal groove, within which slides a bar of iron fixed

are

to the under side of the plank L; thus the upper plank L is steadied and cannot get out of position. When the engine or carriage is lifted, the bar K is hooked into the link i, and the toe of the bar inserted into one of the notches of the plate n; then a man, bearing down the end of the bar, drags the apparatus and engine or carriage towards him, the whole sliding upon the plank M. When the engine or carriage is adjusted over the rails, the adjusting screws screwed back, and the water escapes through the waste holes p, p, when the rams descending, the engine or carriage is placed upon the rails; this object being effected, the water is thrown out of the cistern H, and the apparatus placed in the tender or other place provided for it; in some cases, a single cylinder and ram may be employed with a vertical pump, and for other purposes besides that described, likewise the cylinders may be substituted by screws, the other general arrangements being the same; also pipes or fittings for the water channels in any other suitable way than that shown.

One of the machines may be seen at work (at the manufactory, John's-place, Holland street, Blackfriars' bridge), loaded with a weight of 8 tons, which is lifted one foot high by the force of one man in three minutes; thus the worst accident may be set to rights in half an hour by four men, although the engine may be buried in the soil up to the axles.

I prefer the hydrostatic apparatus from having observed that, when one pair of wheels of an engine or carriage is off the line, when the end is lifted by a jack in the ordinary way, the vibration produced in the act of turning the screw has frequently a tendency to throw the engine or carriage farther off the line; the hydrostatic apparatus, by producing a steady motion upwards, produces no vibration, and it is consequently safer.

In most cases, an accident happens either upon the edge of an embankment or on the side of a cutting, under which circumstances it would be exceedingly difficult to use a screw at all, as the space would be too confined to work it; but the hydrostatic apparatus can be pushed under the engine, either or both rams

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may be forced upwards, so that, in the case of the engine and tender being both off the line together, either may be got on the line, without reference to the other, and with the greatest facility.

The modification with the screw is a very simple and portable apparatus, and should be always carried in the tender, is perfectly adapted for a slight accident, but is not so perfect in its application as the more expensive hydrostatic apparatus. I recommend that a hydrostatic apparatus be kept at each station, so that in the event of a serious accident happening to a train, the most efficient apparatus may be dispatched to its assist

ance.

Traversing Screw-Jack.

Figures 4 and 5 exhibit the screw modification. The screw-jack a is bolted to the plank c; at the other end of the plank is fixed the rack g, in which the toe of the strut ƒ advances as the screw b is elevated; the strut works in a joint in the follower k; the position of the strut when the screw is depressed is shown by the dotted lines. The object of this strut is to relieve the screw of the violent cross strain to which the apparatus is subject, when the engine or carriage is pulled over by the lever; which strain is entirely transferred to the strut, and the screw has merely to carry the load.

The operation of traversing the jack is as follows: by hooking the link i upon the hook of the lever e, the toe of the lever being inserted into a ratch of the rack h of the lower plank, when a man, bearing down the end of the lever, drags the apparatus and engine or carriage towards him with great facility; the same lever is used to turn the screw, and to produce the traverse motion. By this apparatus an engine of 16 tons weight has been replaced upon the rails in five minutes by the engineer and stoker alone; thus those delays which are the subject of so much annoyance and loss to railway proprietors and the public, need not happen in future; the apparatus is exceedingly portable and cheap, and no train ought to be allowed to go out without its being sent along with it; it may be carried either upon

15, Stamford-street, Blackfriar's Road.

W. J. CURTIS.

Sir,-A subject of great interest amongst railway engineers at the present moment is the best means of working the Greenwich Railway free from chance of accident by collision, in consequence of the Croydon train crossing the Greenwich rails, and the expectation of the Brighton and Dover trains coming upon the Greenwich line. The matter is now undergoing investigation before a Select Committee of the House of Commons, and many plans have been laid before them, and more are in the course of preparation to submit to their judgment. One of these is invented and patented by me, and I beg to hand you a description thereof for publication.

The peculiarity of my plan consists in conveying the signal a mile or any convenient distance from the station,

the object being that the engineer may pass the signal post, and have distance and time sufficient to stop the train before reaching the station or place for stopping; the machine for a light is shown in figure 1. A, is a lamp post. C, a lantern of any peculiar shape, with bulls-eyes on three sides, or it may be formed of glass like a street-lamp, or in any other manner. C, is the lamp with reflectors behind the light in the usual way. B, is a shade supported upon the vertical rod e, passing through the post and united by a joint at its lower end, with the bellcrank F, to which is likewise suspended the ball or weight M; to the other end of the crank F, a joint is attached, with which is connected a strong wire g, which is led like a bell-wire, by proper