smoke are prevented from falling into it; as also any fragments off the arch and "tears" are effectually excluded. Farther, the destruction of the furnace cannot be so great as on the old principle, where the arch has first to receive the heat. But should it be

preferred to leave the cistern uncovered there is no possibility of the angles of the bricks falling into it, as the patentee covers the furnace in the manner shown in the engraving, fig. 1, and afterwards more particularly described, with a cone of fire clay in one piece larger in diameter than the cistern. The system of heating from below has also the advantage of considerable saving of fuel and time, as heat is much more easily transmitted through platinum than through fire clay.

Another valuable improvement of Mr. Bessemer's consists in placing each cis

tern

in a separate chamber, whereby each cistern may be removed for casting when ready, without lowering the temperature of the rest. In the present furnaces five minutes are allowed for each of the six cisterns (that being the usual number employed) being cast, and if longer time were taken the last would get cold, and if it were left till the heat was got up again, the glass would be spoiled by the undue evaporation of the salt.

The next improvement we have to notice relates to the annealing oven, and consists in

forming at the bottom of the oven a flat surface sufficiently large for annealing one plate. The oven may contain many such surfaces. Each surface is composed of a number of blocks or hollow tubes, of fire brick or other suitable material, first subjected to a heat at least four times greater than they will afterwards have to undergo. When cold they are fastened or connected together by bolts and nuts, or other means (their sides being ground to fit close,) hollow cubes being preferred for this purpose, as affording facilities for meeting together and giving the required strength with a small weight of materials. These annealing tables or surfaces are ground to a perfect level by the grinding apparatus now used for grinding plate glass. Upon these tables or surfaces the plates of plastic glass undergo the annealing process and are allowed to cool, solidifying in contact with the level surface and thereby becoming equally level. By this

means a great saving is effected, as owing to the very uneven surface of the present oven the plate of glass is often so very much out of the level, and the surface so indented, that

more than half of the glass is ground away before it is in a fit state for sale; and as the duty is paid upon it in the state in which it is brought out of the annealing oven the loss is very great.

We shall proceed now to describe the accompanying engravings, and in the course of doing so shall have occasion to point out several subordinate improvements of a very useful character.

Fig. 1 is a vertical section of a plateglass furnace constructed according to Mr. Bessemer's plan, and fig. 2 a horizontal section or plan taken on the line A B, through the upper openings where the melting cisterns are introduced.

A A is the masonry of which the furnace is composed, being built of fire-stone of the usual description. B is the main flue or chimney, CCCCCC six openings or compartments, each forming distinct furnaces with fire-places, D, to each, and ash-pits, E, under the same. The interior of the furnaces C are lined with fire-brick, and at top of each is a conical cover F, composed of the same materials. These coverings have holes at top communicating with the small flues G, which lead to the main chimney B. The flues G are each provided with dampers. The peculiar form of the top F, of the furnaces C, is of more importance than may at first sight appear. In the process of manufacturing plate glass, as at present practised, a considerable evaporation, as before noticed, takes place during the process of melting, and from the usual construction of the furnace and position of the melting pots placed therein, a condensation takes place on the dome of the furnace, which causes what are technically called "tears" to drop into the melted glass, which produce the most injurious effects. It is to obviate this serious defect that Mr. Bessemer gives to the cover F its conical form (glazing it also on the inside) so that any fluid which may form upon it runs down to the base of the cone and drops outside the melting pot. H H is a circular piece of fireclay, which is moulded to fit the ledge (I) between the furnace C and fire-place D, and upon which it rests, forming a stand upon which the melting pots are placed whilst in the furnace (see figure 3, where these stands are shown on an enlarged scale); there are openings which allow the flame and heat from the fire-place to pass through and circulate round the melting pot. J J are doors composed of fire-brick and strongly clamped together with iron bands which close the furnaces during the process of melting. K is the refining cistern melting-pot, made of the usual material and of the usual form, with

during the refining process are shown in the elevation and plan, fig. 7 & 8:

As soon as the melted glass is removed from one of the furnaces C, the cistern is placed within a metal cylinder S, which is lined with fire-brick to prevent the escape of heat as much as possible, the bottom of the lining being ribbed or grooved so as to form a communication with the opening T in the centre. The top edge of the cylinder S is accurately ground and fitted to the bottom of the cylindrical cover U, which is suspended over it, and as soon as the melting cistern is placed on the cylinder S, the cover U is lowered on to it. Y is an air-pump, which is kept in action by a steam-engine, and communicates with three cylindrical vessels W1 W2 W3 by the pipe V, which form vacuum chambers. To these chambers pipes Z1 Z2 Z3 are attached, which are connected to the valve box a, and which in fig. 7 are shown closed by the slide b; this slide is provided with a spring and has an opening, C, in the centre to form when moved over the openings of the pipes Z (by turning the handle e), a communication between the valve box and the vacuum chambers; but when placed in the position, as shown in fig. 7, a communication is formed between the valve box and the atmosphere, which will allow the air to flow into the cylinder S, by means of the pipe d, and the cover U to be lifted up; e is a handle, the spindle of which is screwed and works in a box f, and by this means the valve is moved backwards and forwards. The object of this apparatus being to extract any air or air bubbles that may be left in the melted glass after it has been removed from the refining furnace, previous to its formation into a plate, it will be evident that if a vacuum is maintained in the chambers or vessels W1 W2 W3, that the air contained in the cylinder S and cover U must rush into the vessel W1 by the pipe Z1, whereby its density will be lessened in proportion as the vessel W is larger than the vacant space in the cylinder S and cover U. The further rotation of the handle e will bring the slide b over the second pipe Z, closing the communication between the cylinder S and vessel W, and establishing a communication with the vessel W2, and cylinder S, the small remaining portion of air left in the cylinder S again divides itself equally into the increased space thus formed. The still further progress of the handle e brings the slide b over the opening of the last pipe Z3, and closes the communication with the chamber W2, whereby the minute portion of air left in the cylinder S and cover U again expands itself into the increased space thus formed between it and the chamber W3. By this

arrangement of having chambers ready exhausted, an almost perfect vacuum is formed in much less space of time than if the operation had to be performed by the air pump in direct communication with the cylinder, after the cistern had been placed in the cylinder. The atmospheric pressure being thus removed from the surface of the melted glass the globules of air contained therein will become greatly expanded, and thereby acquire sufficient floating power to rise to the surface, and this operation requiring only about two minutes, the glass suffers scarcely any loss of heat, and is now in a perfect state for casting.

The construction of the improved annealing oven is shown separately in figs. 9, 10, 11, and 12, each of which however, represents but one seventh part of the area of the oven. It consists of a number of square blocks,

which are hollow and open at bottom (as particularly shown in figures 11 and 12.) They may be made of any size to suit the form of the oven, as may be most convenient, but the patentee prefers that they should be about two feet square. The sides are ground and fitted to each other, and they are connected together by screws and nuts, grooves being formed in the sides of each block, into which clay or cement is forced to prevent shifting, as shown at tin figs. 10 and 12. As soon as the whole is fitted together it forms a surface on its upper side, as shown in fig. 9; and previous to its being placed in the oven it is subjected to the ordinary grinding machine and made as level as possible, after which it is set in sand in the ordinary way. In some cases it may be desirable to have moveable bottoms to the annealing ovens, and for that purpose the patentee provides rollers kk, as shown in figures 13, 14 and 15, upon which it can be moved in or out as occasion may require.

The claim of the patentee as regards the improvements we have described is as follows:

First, to the forming of furnaces in such manner of solid masonry in the centre and with separate chambers and fire-places arranged round that solid centre, as that each cistern or pot may be heated independently of its neighbouring cistern or pot, and withdrawn from the furnace to be emptied of its contents, when the glass contained therein is in a fit state for being operated upon without affecting the temperature of the other pots or cisterns in the furnace, as shown in figs. 1, 2, 3; as also the conical-shaped covers placed over each separate furnace, and glazed inside to prevent the falling of tears into the

melted glass. Second, the introduction of a platinum bottom to the cistern or pot, and the application of a top ring thereto, as shown in fig. 4; and the perforated ring on which the cistern or pot rests, as shown in fig. 3. Third, the mode of skimming by means of the top ring and handled cutting plate, shown in fig. 6. Fourth, placing the cistern or pot in a vacuum, in order to exhaust the air from the glass contained therein, previous to its being poured upon the table, as shown in figs. 7 and 8. Fifth, the annealing table (the various parts of which the patentee prefers to be of fire-brick, but which may be made of stone of any suitable kind to stand great heat) united together so as to form one solid mass, and ground or otherwise brought to a perfectly level surface, as shown in figures 9, 10, 11 and 12, 13, 14 and 15.

PROGRESS OF FOREIGN SCIENCE.

Belgian Publications on Prevention of Accidents in Mines-VentilationThe Safety Lamp, &c.

The Government of Belgium has, within the last few years, set a noble example in endeavouring to elicit all the information that science and experience can produce, with respect to the deeply important questions to that country and to our own, which relate to the best and most effective and practical methods of diminishing the dangers which beset the miner, in coal-pits which are subject to fire-damp. Much as has been effected in our own coal-fields, by the science of such men as Davy, Clanny, and Stephenson, and by the practical skill and judgment of engineers of the class of Buddle, lamentable accidents are even yet of frequent occurrence; but the special conformation of our great coal-fields gives facility for ventilation (the great antidote to fire-damp accidents), which the different structure of the Belgian, and most of the other continental coal measures, does not present.

With a most laudable anxiety to meet these difficulties-to place before the public, for the common benefit of allwhatever had been done in Belgium or other countries, in improving the working of mines troubled with foul air, a Royal ordonnance, of the 22d of June, 1839, founded on a Report of the Minister of Public Works, M. Nothomb, decreed that a sum of two thousand francs should be placed at the disposal of the

Royal Academy of Brussels, to found a prize for the best essay on this subject. Government further provided the requisite funds for the publication, in a cheap form, of such of these essays upon the modes of working coal mines subject to foul air, as should be deemed by the commission of the academy worthy of selection for the purpose.

men

The result was, that fourteen essays were received; some of these were by whose ardor scribendi outran their knowledge of their subjects; but others were considered, and justly, as of great merit. In May, 1840, the Academy heard the report of M. Cauchy, one of the Commission appointed to examine the essays, and determined that in consequence of the publication between the time of the prize being offered and the receipt of the essays, of an elaborate paper, by M. Courbes, in the Annales des Mines, on the same subject, the prize of two thousand francs should not be awarded; but that three gold medals, of eight hundred francs value each, should be given to the authors of the three best essays, and two medals in silver to the next in merit, that these five essays should be published at the expense of the state, and fifty copies given to each of the authors, along with the report of the Commission upon safety lainps, instituted at Liege. The essays were all sent in under epigraph signatures-the names of the authors not being known until after the decision. The five memoirs, together with the report upon improved safety lamps, are now published, and constitute a single 8vo. volume, containing a mass of systematized information that, if translated into English, could not fail to be of the highest value to those of our countrymen who are engaged in coal workings, and of whom it must be admitted, that however great and unequalled may be their practical skill, energy, and courage, guided by a judgment the most prescient, still, as a class, the amount of correct and exact scientific knowledge, upon the matters of their own avocations, possessed by them, is comparatively small.

To attempt an analysis of this closely printed volume, so abounding in details, would be impossible; the best idea that we can give of the sort of matter it contains will be by a specimen, and we choose one, passim, and will take part of