by which the fire-grates are moved in or out from under the boilers when the latter are in or out of use.

hh, &c., stop valves, by which the communication of any one boiler with the steam pipes k k, which are common to them all, may be cut off at pleasure. ii, man lids to the boilers.

, the feed pipe for supplying the boilers with water from the feed pumps wrought by the small engine, 5. This engine is worked by steam from the great boilers; its office is to feed the boilers and open the valves no p, by means of the cams, upon the cam shafts 6 6. 4 is the suction pipe of the feed pumps, which draws out of the hot well, 8, into which the condensed water from the condenser flows by the pipe 2; the overplus passing off by the drain 3 3.

m is a long tube of boiler plate of large diameter, placed in the smoke place or tunnel e, and which is always full of water; the feed pump discharging into it at one end, and the feed delivering into the boilers at the other, so that the feed water passes into them nearly boiling.

n, o, and p, are double-seated valves, moveable either by hand from the engine room below, or by the cams wrought by the engine, at pleasure. The offices of these valves are as follow:-when n and o are both open, and p shut, steam is free to enter the condenser, T, from the boilers; n being closed, and o continuing open, with the jets of water playing into the condenser, a vacuum more or less perfect is formed in either the right-hand vacuum vessel V' V', or in the left-hand one, V V; n and o being both closed, and p opened, the vacuum vessels are placed in alternate communication with the railway main s, by means of the pipes rr, and share their vacuum therewith.

ww, the water main and stop valve by which the jets of condensing water are admitted or cut off from the condenser T, during the whole time of one set of exhaustions of the vacuum vessels. These jets of water are kept constantly playing into the condenser. The condensing and condensed water are withdrawn from the condenser by means of the large syphon tube, 2 2, whose total height from the surface of the water in the hot well, 8, to the bottom of the condenser is at least 34 feet. The water, therefore, continues freely to flow off from the extremity into the drain 3 3,

but no air can enter the condenser by the same pipe.

xx are similar syphon pipes, but of a much smaller size, to relieve the vacuum vessels of the small quantity of condensed steam which will be produced in them by the contact of the steam blown into them, with the wood lining of their sides.

All the vacuum vessels, as well as the condenser, are lined with wood and jacketed outside, in the way particularly shown in figs. 3 and 4, so as to reduce the condensation by contact of the vessels as much as possible, inasmuch as in the case of the vacuum vessels all cooling, and in that of the condenser all heating, will be attended with waste of steam.

y'y', yy, are the snifting valves of the two sets of vacuum vessels.

zz, the much smaller snifting valve of the condenser.

It appears to be immaterial at what level of the vacuum vessels the steam is blown in, provided it be blown very rapidly in, so as not only to displace the air and discharge it at the snifting valves, but to expand it and cause it to pass out by its increased bulk. From the very small difference in specific gravity that exists between steam at 212° and common air at 50° or 60° Fahr., and from the tendency to mutual diffusion, it is quite a mistake to suppose that in vessels of great capacity any distinct plane of separation can be preserved between steam and air. In comparatively small vessels a separation may be observed; but in large vessels, if the steam be blown in slowly enough to preserve such, mutual diffusion takes place; if rapidly, mixture; but if very rapidly, the air is driven out before the steam. This being the true principle of "blowing through," it is not important where the steam is admitted, provided the vacuum vessels are of a long tubular form, and that the passages for the egress of the air be at the ends remote from the steam entrance. I do not, however, confine myself to a horizontal position for the vacuum vessels, nor to any particular place for admitting steam. At first it occurred to me to have two very light disks or diaphragms, which without touching the sides of the vacuum vessels should, on the admission of steam, be driven before it, and parting from the centre aperture at o, right and left, pass to opposite ends

end of each boiler). The grate rests upon a complete frame of cast-iron, carrying with it the fire-door, i, and lined all round inside, or next the fuel, with fire-brick. This frame is made to traverse on the rollers, c c c, either from c to p, or vice versa, by means of the wheels and pinion, r d, in dotted lines, outside the setting, and connected with the toothed pinion and roller, c', taking into a rack attached to the frame, 66.

f is the ash-pit under the grate, formed to be cleared by the rake, g, which draws the ashes down into the ash-tunnel, n, whence they are removed without interfering with the draught.

m is the cold-air tunnel to supply draught to the fire, through the grated ventilator, nn, which is made to open or close by the lever and balance weight, po. yz, the directing plate for the entering current of air.

e is the bridge; t t, the internal flue; v, the lower flue under boiler bottom; w, the entrance therefrom to the side flue.

The boiler is at work in the position of the fire-grate, &c., shown in the figure, and the air to supply it passes up through the ventilator, n n, and taking the general directions shown by the arrows, passes under the grate, 6 6, and through the fire, &c.

When the boiler is not required to generate further steam for a time, the fire and fire-grate are withdrawn or moved back from under it by the wheels, r d, &c., and run back under the fire-brick arch A, until the internal fire-door, i, comes in contact with the frame of the outer one, k. Fresh fuel is now thrown on, and all the doors, ik, and the outer air-doors, 1, closed home.

In the act of running back, the firegrate, 6 6, the stop, q, strikes the lever, pp, and shuts off the supply of air to the fire through n n. The fire can now no longer burn freely, but the heat radiated from its upper surface, in place of being expended in generating steam immediately in the boiler, is now absorbed by the brickwork of the arch, A, which becomes red-hot.

If things were preserved long enough in this state, the fire would go wholly out, but as these boilers are required at intervals of from half an hour to an hour or so, this does not occur. Steam is now

again required; for this purpose the firegrate is again run forward under the boiler, as shown in fig. 6; in doing so, the air is re-admitted through nn; and by the directing plate, y z, the currents are caused to sweep under the surface of the heated arch, A, and side-walls of the chamber, dk, the whole of the heat of which is thus carried away and swept through the flues of the boiler. Thus, by this arrangement, the heat of the fire that would be otherwise lost between the times of trains is husbanded by being absorbed by the brickwork as in a magazine, and is at once when wanted given back and made use of. It is obvious that this construction of boiler is applicable to every operation requiring the intermittent use of large volumes of steam, as well as to the existent mode of exhaustion upon atmospheric railways. fire-place should be so proportioned that the fuel shall need no poking or raking, and no supply except at the intervals when drawn back under the arch, A, when the bars may be cleaned; a large deep body of fuel, slowly but perfectly burnt by a sufficient supply of air, will be found always to give a more economical result than what is called "thin firing" with continual stoking.

The

The top of the boilers are covered to the depth of some inches with sifted ashes, s s, as jacketing.

66

At the end of Mr. Mallet's Memoirs there are four Supplementary Articles, illustrated by plates-the first containing an account of a mode of obtaining vacuum by a combination of the method of direct condensation of steam with that of the displacement of air by water; the second, a design as originally made for water-vacuum vessels, or apparatus for obtaining vacuum for atmospheric railways by the employing of vessels of water by tubes of more than 34 feet in height on the Toricellian Principle;" the third, "the details of a new long valve and main for atmospheric railways," and the fourth, "details of an arrangement for releasing the head of the tra

velling piston instantaneously, in case

of accident in the line or to the train." The last two appear to us eminently deserving attention, and we shall hereafter also give them at length.-ED. M. M.

E

Having spun a yarn upon stoves, now comes another upon grates. After examining and experimenting upon most kinds which have been invented, the conclusion I have come to is, that the best for general use is that called the Kennard, but which might more properly have been termed the Rumford, and it could be shown to have been used by the late Sir John Robison even previously. The merits of this grate are economy, a good draft, with great heating power, owing to the use of fire-brick. Its compact neat form, or the more polished bright appearance which can be given with a great degree of elegance, should also be added as recommendations. As long as the public are satisfied with paying a larger price for a less efficient article, the manufacturers cannot reasonably be expected to press into notice a less costly one. Such is the case with this grate. But a man can fit up his principal rooms with costly grates on this principle, for the fire-brick is the main thing, while the rest of the house should have the really useful. The grate I refer to does not require a minute description, it is coming into such general use. It has a bevelled metal front contracting the fire

place to a smaller space, while the sides and back are lined with fire-bricks about 3 inches thick, and made in three parts. These grates should be less bevelled in and kept more to the front; the front of the fire should be even without the perpendicular line of the inside of the chimney (I speak of Scotch 3 feet walls); the width from the front bars to the back brick should be less, never exceeding 8 inches, while the length of the firebars should be extended if more heat is required. With these precautions, I found rooms which were intolerably cold, with huge fires in other grates, made as warm as possibly could be wished with much less coal. Mr. Steele, of Edinburgh has introduced an excellent plan for a lid which totally excludes back smoke or soot when a fire is not required; this should be used in all these grates. To be used most economically, these grates should, after blazing well up, so as to heat the room, be covered with dross, and so left till the evening circle draw round, when one blow causes a blaze.

There are many much more showy grates which may have some little advantage in one particular point, but divested of this pretension, are not equal to the kind mentioned, while there is no comparison in point of cost. In the one,

nothing can be obtained under two figures, whereas in the other it requires some ingenuity of design to raise the price above one figure. I have seen statements by able men about some grates being good ventilators; but they have mistaken attempts at circulation of heated air for ventilation. The fact is, all grates are bad ventilators, as the best are low; while the air is generally admitted low also, and makes its most direct way to the fire, without kindly making a circuit of the room. Ventilation must be otherwise arranged, and requires, together with lighting, and the supply of water in private houses, to be brought more into practical notice. Mr. Sylvester, as also Mr. Steele, have done much for all sorts of grates. I refer particularly to the kitchen range of the latter, with which I am best acquainted. I by no means wish to derogate from that of Sylvester; but Mr. Steele's can hardly be surpassed. Sylvester has thrown out plans for still further im

provements in fire-places, especially that of carrying the vent down, as well as up. This should be done in all new houses, in the principal rooms. Another improvement of his is the folding bars for regulating the draft. I have to conclude by suggesting the modification of his plan represented in the prefixed engraving.

Description.

A is the chimney-piece.

B, the fire-place, sides and back of fire-brick.

C, the smoke vent, with iron shutters. D, a drawer, which can be pulled out, and into which the soot falls.

E, the chimney, which is built up to a proper size, and is bevelled off to allow the soot to fall into D.

F F F, iron, polished or not; F2, polished to reflect fire.

G, shape round fire-place, covered with tile, or ornamental iron work.

The advantages would be, full benefit of the heat, power of regulating the fire and sweeping the chimney without annoyance. The whole might, as suggested, be highly ornamented, or plain and neat. FORESTER.

ON THE METHOD OF COMPUTING THE TIME AT ANY PARTICULAR PLACE, AND ALSO THE DIRECT DISTANCE BETWEEN ANY TWO PLACES WHOSE LATITUDES AND LONGITUDES ARE KNOWN.

Sir,-At page 370, vol. xlii., there is given an abstract of a paper by Benjamin Lewis Vulliamy, Esq., on the Construction and Regulation of Railway Station Clocks. This paper was read at a meeting of the Institution of Civil Engineers; and, in consequence of the great importance attached to the subject, it led to a very animated and interesting discussion among the members of that body who happened to be present at the time the paper was read. The same paper, moreover, suggested another, page 410, of the same volume, continued at page 417, on the method of computing the time at any particular place, by means of data derived from observations of the sun or a fixed star; this was likewise followed by a second paper of a similar character, page 4, vol. xliii., for calculating the direct distance between any two places on the surface of the earth of which the latitudes and longitudes are known.

These two papers were drawn up with the best of motives, and with the utmost

degree of unassuming modesty and candour, holding out no pretensions of any kind, and claiming only the very humble merit of endeavouring to direct the attention of your readers to the solution of two important problems in spherical trigonometry; but certainly without the writer thereof entertaining the most remote idea that they would either require remarks, or be deemed sufficiently meritorious to deserve them. They have, notwithstanding, been animadverted upon by one of your correspondents, who has frequently figured as a critic, or rather hyper-critic, in your pages. In the present instance, however, the wrangler has thrown down the gauntlet in vain; for no one feels disposed to take it up; and your humble servant, the writer of the condemned papers, although he has long enjoyed a considerable share of notoriety in the list of contemporary authors, has never yet condescended to notice criticisms on any of his numerous works, whether favourable or the reverse, well knowing that those who arrogate to themselves the office of judges or censors in cases of this nature, are not at all times the best qualified for the purpose. It will, therefore, be seen, that there is no intention on the part of the writer to enter the arena of disputation, for neither his means nor his inclination will admit of it; and he feels disposed to accord to "KINCLAVEN" the justness of his remarks, as far as they are just. His sole object, therefore, in taking up the pen on this occasion is, to examine the several circumstances of the case; and, by making a fair and impartial comparison of the results, to let them stand or fall according to their deserts.

Recurring to page 410, vol. xlii., and attentively examining the premises there laid down, it will at once appear for what purpose the subject was undertaken, and for what reason the method there employed was adopted; but, in order to avoid the trouble of reference, it will be proper to repeat the passage that bears directly on the point. It is as under :

"The method of resolving this problem by reference to the circles of the sphere, is the true and legitimate method by which the solution ought to be performed; this, however, presupposes a knowledge of the projection of the different circles that can be drawn on the surface of the sphere; and this is the very point which constitutes the difficulty and mystery of the subject. In order, therefore, to avoid this difficulty, and to render the steps of investigation as plain" as possible, we shall adopt the principle of development, as by this means the calculation requires nothing beyond the rules of plane trigonometry."