attendant may turn at pleasure. To prevent the escape of any infectious matter from the bed, the front only is left open. The opening may be increased or diminished at pleasure by the raising or depressing of the curtain at the top. It is clear that there must be a stream of pure air constantly passing into the bed, and that any one standing immediately in front is as completely exempt from all noxious influences, as far as that patient is concerned, as if he were at many miles' dis

tance.

An experiment on this principle is at length in the course of being made in the Glasgow Fever Hospital. In ward 8th of that establishment, which consists of two patients' apartments, each twenty-four feet square by twelve in height, and a separate smaller room for the nurse, a stove in the fireplace of the latter is supplied with air solely by a pipe communicating in branches with apertures in the ceilings of the patients' rooms. There is accordingly a draught of air from the top of each of the patients' rooms, and this is so powerful, that on the two rooms being filled with dense smoke from wet straw, they were completely cleared in thirtyfive minutes, the aggregate contents of the two being 14,000 cubic feet. It is obvious that the arrangement, although a great improvement upon no-ventilation, will only be complete when there is a particular draught from the top or back of each bed; in which case alone will the medical attendants and others be exempt from the contact of infectious matter. While we are writing the present sheet, the authorities connected with the hospital, satisfied so far with the experiment, are about to extend Mr Fleming's mode of ventilation to the whole establishment; it is to be hoped that they will not rest content with a tube opening in the ceiling, but extend one to each bed.

A description of the arrangements made by Dr Reid in the Houses of Parliament involves the principles of heating, or rather of temperature-regulation, as much as those of ventilation. The present House of Lords is a portion of the old palace of Westminster, which was formerly called the Painted Chamber. The House of Commons is the building which, down to the conflagration in November 1834, was used as the House of Lords. They are contiguous; and beneath both there is a series of vaults, part of which (beneath the old House of Lords and present House of Commons) were those in which the gunpowder conspirators had deposited the means of blowing up the Parliament in 1605. It is in these vaults that science now conducts a signal example of one of her most striking though most simple triumphs. One vault is devoted to the purpose of introducing and purifying the air, which is done by means of a wide space towards the public street, covered with a piece of coarse gauze, to stop as much as possible of the soot and dust with which the air is necessarily loaded in the centre of a large city. Having passed into the vaulted apartment, it is completely washed with water as it rushes across to the passage beyond. The washing apparatus consists of a number of pipes laid longitudinally and transversely on the floor; each pipe is perforated with a great number of holes, and from these spout jets d'eau in all directions, so as to fill the apartment with an intense spray, and effectually wash the air as it proceeds through it. On the inner side of the vault the air is as fresh and pleasant as at the brink of a waterfall. Being thus purified, the air, if necessary, is made to pass through a vaulted chamber, containing a congeries of pipes of hot water; and being there warmed, is sent on by a channel or passage to the House. The temperature of the air which is admitted can be at all times regulated with perfect nicety, by allowing it to go, more or less, through the warming-room; and for the purpose of discovering at any time what is the degree of heat the persons above are enjoying, a thermometer is pulled down by a string from a concealed part of the house.

The air, thus regulated in temperature, is admitted into the house through canvass which covers the walls,

and also behind the bar, seats, and tables. The s vass, which is stretched upon the walls, or rather at a little distance from them, is of a thin yellowish deserg tion, and is streaked or marked to resemble oak paar As high up as the heads of the members, the chova is papered in a neat style. When the air adinuted a this manner all round the house, through the texiam of the canvass walls, has been breathed and vitiated, passes off through ventilators in the roof into a king garret, whence it proceeds along a passage, and dramas. a shaft to the ground. On going round by a stair to the bottom of this very strange air channel, we find selves in a vestibule opening upon an immense a-hinto which we perceive red hot cinders occasion. falling. We step forward, and enter the ash-pit. V now find ourselves standing at the bottom of a rec chimney, measuring a hundred feet high, and erin feet broad at the base, and in which, at the hegu e some twelve or fifteen feet overhead, we observe a large blazing fire suspended on a capacious grat There is no opening into the chimney except from te vestibule, into which all the vitiated atmosphere of House is poured-the fire being trimmed only by m of a small door on the outside, but which is usually shut-and therefore this forms the great organ draught in this extensive ventilating apparatus. For the House of Commons, the air is admete through gauze into a lower vault, in the same man as for the Lords; passes, if required, through a heate room, and is thence conducted in a purified state t space beneath the floor. For its admission, the fi sz and rising steps are penetrated with millions of se holes, and rising in these, it passes through a es~*~* carpeting into the house. Having there performed office, the air passes off by openings round the edges the panels in the ceiling, into a garret above, where is led away by a passage to the descending channi the ash-pit and fire which have already been desert and which answer for both Houses. In the gr there is a passage containing a sash-window, which 19 sists in regulating the supply of air and dranght. ordinary circumstances, the opening through fresh air is supplied to the House of Commons a 60 cubic feet to pass in at the rate of 10 feet per wee 60 multiplied by 10 makes 600 feet per second, and i again multiplied by 60 seconds, gives 36.000—chst z thirty-six thousand cubic feet of fresh air s every minute for the consumption of the House. air, likewise, can be admitted in either a cold or waru, moist or dry state, at a moment's notice. On one ... sion, seventy gallons of water were sent in in the of moist air in the course of a few hours. The for of the members being very various, the regulator these details, as may be supposed, is a matter of et treme delicacy. The great object desired by the le superintendant is to afford at all times a profuse ply of the best air for breathing, without any sens feeling of draught to the members; and this he se to have admirably accomplished by his ingens rangements for both Houses. It has been aleged, th the method of admitting the air through the cars on the floor has the effect of raising a dust in the apart ment; but such is not the case. Every precautier taken to avoid this, not only by the universal p but by the plans adopted for brushing the feet of members as they pass along the passages and lottes It is further necessary to observe, that the plaus, the best, are only preparatory to others of a more per fect kind in connexion with the new Houses of Par ment now in course of erection, and for the supera dence of which Dr Reid is now necessarily resident the spot.

It is abundantly evident that the choice of a mad ventilation, and also its minor arrangements, must efsbe determined by considerations of local convenergy and of economy. A factory and a steam-vessel prest: an ever active furnace or chimney, into which a far: ventilation can be conducted. In these situations, a/ cordingly, there may be ventilation absolutely wit

a fan or pump can be readily obtained, but in that case the power is both a matter of cost, and it requires attention to regulate it. Generally, therefore, though not perhaps in all instances, the plan by fire or chimneydraught will be preferable in such situations. Where there is an apparatus for warming as well as for ventilating, and where economy is an object, the draught might without much difficulty be effected by the fire winch is used for the former purpose. It would only be necessary to conduct flues from the various roonis down to the ash-pit of the furnace. In this case, however, there would be a certain loss of control over both processes. In buildings already completed, there might be a tolerably efficient ventilation obtained by flues condneted into the kitchen chimney, which, being always active, would keep up a nearly unvarying draught. Dr Arnott has suggested that the fresh air in entering might be heated to nearly the desired temperature, especially in churches and other crowded places of assembly, if the flues for its admission were made to pass longitudinally through the centre of those by which the used air was passing out. Another and simple mode of draught has been practised in connexion with the hotwater warming apparatus, consisting merely of a flue into which a small coil of the hot water-pipe is introduced. This small coil, situated in the flue, and near its bottom, acts precisely like the fire in the chimney for Ventilating the Houses of Parliament.

For obvious reasons, the admission of warm air is generally at the bottoms of rooms, while the used air is drawn off by apertures in or near the ceiling. Mr Perkins, it appears, pursues exactly the reverse plan, conceiving that it "introduces the warm temperature sensibly, and removes the impurities of the room more effectually." Mr Alfred Ainger, an architect, also adopts this plan; he remarks that," with upward ventilation, a great part of the vitiated atmosphere [of crowded rooms] being specifically heavier than common air, is liable, by the slightest check or condensation, to be thrown down and mixed with the air which is already partly unfitted for the purposes of life. But let the ventilating current descend, we have a bright atmosphere consisting of an immense reservoir of pure air, arriving immediately at the lungs, and which, as it becomes contaminated, is drawn downwards by a force with which most accidents will co-operate."*

་་་་་་་་་་

GAS-LIGHTING.

The existence of an inflammable air, as a natural production, has been known from a period of great antiquity. It was observed to issue spontaneously from fissures in the earth; and we are told that it has been employed in such situations, as a source of light and heat, both in ancient and modern times.

This natural gas is also found in abundance in some coal mines, where, being liable to mix largely with the air when ventilation is defective, it constitutes the "fire-damp" so destructive to the miner. From an old wrought-out seam at Wallsend colliery, "a discharge of this gas takes place, through a four-inch metallic pipe, of two cubic feet per second. The pipe is carried up as high as the head-gear above the shaft; and from its orifice issues, with a roaring sound, the stream of gas, which, having been ignited, forms a flag of flame seven or eight feet in length, conspicuous by day, and at night illuminating the entire neighbourhood."

The artificial production of an inflammable air from coal is first mentioned in a letter by the reverend Dr John Clayton of Kildare to the Honourable Robert Boyle, who died in the year 1691. In this letter, published in the "Philosophical Transactions" for 1739, he states, that he distilled coal in a close vessel, and obtained abundance of gas, which he collected in bladders, and afterwards burnt for the amusement of his friends. Richardson on Warming and Ventilation, p. 78.

It was only, however, esteemed as a philosophical curiosity until the year 1792, when it attracted the attention of Mr Murdoch, an engineer, then residing at Redruth in Cornwall. In that year he commenced a series of experiments on the gases obtained by the action of heat upon coal, wood, peat, and other inflammable substances, and actually prepared coal-gas on a scale sufficiently large to light up his own house and office. Five years after, while living at Cumnock in Ayrshire, he again erected a coal-gas apparatus. In 1798, he was engaged to put up his apparatus at the manufactory of Messrs Boulton and Watt, Soho, near Birmingham, where he continued to experiment, with occasional interruptions, until the year 1802. It does not appear, however, that much attention was excited by these first efforts at gas-lighting, except among a very few scientific individuals, until the general illumination at the peace of Amiens afforded an opportunity for a more public display. On this occasion, the front of the manufactory was brilliantly lighted up by the new method, and it at once attracted the wonder and admiration of every one who saw it. "All Birmingham poured forth to view the spectacle; and strangers carried to every part of the country an account of what they had scen. It was spread about everywhere by the newspapers; easy modes of making gas were described; and coal was distilled in tobacco-pipes at the fireside all over the kingdom."

By the exertions of a Mr Winsor, a company was formed for supplying London with gas; but it struggled for many years with the difficulties at once of inexperience and public prejudice, and was a source of loss to many individuals. At length most of these difficulties were overcome, and gas-lighting began to spread over the kingdom. Its progress in dwelling-houses has been retarded by several considerations, most of which are now in a great measure overcome. It was injurious to delicate furniture, and to many of the wares exposed in shops; it often caused headaches when used in close apartments; and, above all, it was dirty, and had a most disagreeable smell.

Science, however, has not been deaf to these complaints urged against the obnoxious qualities of her gift; by means of the joint labours of the chemist and practical engineer, all reasonable grounds of objection have been long ago removed; and the art is now so perfected in our best gas-works, that it is doubted whether much remains to be discovered either for simplifying the process or improving the quality of the product.

It is true that unburnt gas has still a disagreeable smell, but this, instead of being an evil, is in reality a most valuable property; it thus gives warning of its own escape, at once directing the attention of the consumer to his stop-cocks or fittings, without some imperfection of which, the smell of gas cannot be perceived.

The success which has attended gas-lighting whereever it has been introduced, has now effected its adoption in almost every town in Great Britain. The continental nations are slowly following our example, where coal can be obtained. In America, it is used extensively in the large towns; and it has even reached the remote colony of New South Wales, the town of Sydney being now lighted in this manner.

The employment of gas at a distance from towns is limited by the expense of the apparatus compared with the quantity of light required; but where the annual expenditure for light is not less than £40, it is probable that gas might be made with advantage.

The employment of gas made by the decomposition of oil was at one time common. It had two great advantages over coal-gas, namely, a greater brilliancy of light, and a much simpler mode of preparation. These qualities, however, have not enabled it to compete with the superior economy of its rival; and it is so fast

Where dimensions are stated, they are taken from a mall gas-work belonging to a town of 5000 inhabitants. A represents the retort, of which several are commonly use at once. It is a cylindrical or D shaped vessel of clay or cast-iron, about 8 feet in length and 20 inches internal diameter. It is built horizontally into a furnace, either singly or otherwise, in such a way that the are can act completely around it, so as to keep it at a full red heat. Iron retorts have, until of late, been almost exclusively used, but they are inferior in almost every respect to the clay retort which has been lately introduced. For instance, the latter is only one-third of the cost of iron, and we state with confidence that it s more durable, that it can be heated with less fuel, that it is easier kept at a uniform heat, and that it consequently produces a larger quantity of gas.

The retort, whether of clay or iron, has two openings both external to the building; one of them is the end of the cylinder, which is furnished with a closely-fitting Lid of iron; the other is an aperture in its upper surlace for the exit-pipe, which passes from the retort to B, a vertical section of the hydraulic main-this is a round or square vessel of iron about 10 inches by 14 in size. It passes above and in front of the whole line of retorts; it is half filled with liquid, into which the exit-pipe dips; it serves to collect the gas and other matters from any number of retorts, and to cut off its escape by any retort which may be open. It is connected by means of a wide pipe with C, the tar-cistern, in which the tar and everything deposited from the gas by cooling is collected. From the tar vessel a tube rises in a sloping direction to D, the condenser-a series of tubes through which the gas is made to pass, that it may be thoroughly cooled. To the condenser there is sometimes attached E, an upright cylindrical vessel filled with brushwood, through which the gas passes before it is sent to F, the chemical purifier. There are usually several vessels of this kind, and of various forms; they contain quick-lime, either dry or mixed with water to the consistence of cream. From the purifier a tube passes to the bottom of the tank in which G, the gasometer, is suspended-this is a large vessel of sheet-iron for holding the gas.

The retort being heated to a red heat, the charge of coal, about 200 pounds or upwards, is quickly shovelled in, and immediately gives off dense smoke and flames. The mouth of the retort is now closed by its lid, which extinguishes the flame by shutting off the air, and leaves no outlet for the dense vapours arising from the coal, except by the exit-pipe; they rush through this tabe, and are heard bubbling up into the hydraulic main until the charge is exhausted.

It is of importance in this part of the process to attend to the temperature of the retort; for if it is too hot, some of the heavy gas will be decomposed, depositing part of its carbon, and forming light carbureted hydrogen; if, on the contrary, it is not of a certain temperature, there will be formed a large proportion

is also essential to draw the charge before it is quite exhausted, as the last portions of gas consist chiefly of hydrogen and carbonic oxide, both of which, as already stated, have a most injurious effect upon the quality of the whole product.

The time required for a charge of cannel coal is from three to four hours. As soon as one is withdrawn in the form of coke, a second is thrown in, the process being thus continued uninterruptedly night and day.

The dense vapours which pass from the retort into the hydraulic main, consist of coal-gas, mixed with tar, water, naphtha, salts of ammonia, carbonic acid, sulphureted hydrogen, &c. Being subjected to a process of cooling in all parts of the apparatus as far as the brushwood-box, the impurities are condensed, with the exception of the carbonic acid and sulphureted hydrogen; and from the sloping or descending direction of the apparatus to the tar-cistern, they collect in it, and are pumped off as occasion requires. A considerable quantity of carbonate and sulphate of ammonia is also deposited in the tubes of the condenser in a crystalline form, and requires to be cleared out periodically. This is easily accomplished by passing a current of steam down each pair of tubes, by which these salts are at once dissolved. The gaseous matter still retains particles of tar mechanically mixed with it, from which it is freed by being forced through the brushwood vessel. It is now made to enter the chemical purifiers, where it is either washed by agitation with a mixture of quick-lime and water, or is passed through a succession of trays covered with thin layers of this substance in a slightly moistened state. In this process the lime combines with the sulphureted hydrogen and carbonic acid, forming hydrosulphuret and carbonate of lime, which, being both solid, are retained, and the gas now purified is at once passed into the gasometer, where it is stored for nightly use.

DISTRIBUTION OF GAS.

The distribution of the gas from the gasometer to its places of consumption is effected in cast-iron pipes called mains. They are cast in pieces of from 4 feet 6 inches to 9 feet in length, according to their diameter, and are jointed together to any required length. The diameter of the mains varies from 14 inches to 16 or 18 inches, and depends in every case upon the quantity of gas required to flow through them, taking into account at the same time the distance it has to flow, and some other data of less importance--such as the elevation above or below the horizontal line, the curvatures in the pipe, the specific gravity of the gas, &c., all of which are matters of exact calculation to the practical engineer.

The pipes branching from the mains to supply gas to dwelling-houses or manufactories are called servicepipes. They are commonly made of wrought iron or pewter, and vary in diameter according to circumstances.

Throughout all the ramifications of the fittings, the pipes have, or should have, an inclination to the main, and the main itself should incline towards the gaswork. The necessity for this arrangement arises from the presence of watery vapour in small quantity in the gas; being condensed into water in the pipes, it naturally collects in the lowest part, and at last interrupts the continuous flow of gas, so as to cause a flickering of the flame in the burners. Where the proper inclination of the pipes cannot be attained, this is obviated by placing a stop-cock and pipe at the part where liquid is apt to collect, so that it can be let off from time to time as it accumulates.

The quantity of gas charged for by gas companies was at one time regulated by the number and kind of burners employed, and the time they were allowed to burn; but this was everywhere found to be a most uncertain and unsatisfactory method of guessing the consumption by any individual. It is now obviated by the use of a very simple and ingenious instrument