Of the many questions that merit attention and study in connection with the Turkish bath, all sink into insignificance by the side of that of the heating and the nature of the heat supplied in the sudatory chambers. Other things being equal, it is, after all, the heating that distinguishes one bath from another on the score of excellence. The heating of the "bath" is the Alpha and Omega of the whole matter.

There are two ways in which heat may be applied to the body—by direct radiation, as from the sun or an open fire; and by convection, as through a volume of air.

The ancient Roman bathers, with floors below them which rested upon pilÆ, or little pillars of brick or tile, around which the flames and hot gases from the furnace played, and surrounded by heated, hollow walls, evidently submitted themselves to the action of a heat that must have been of a purely radiating character.

So, also, in a less perfect manner, the Turks, who employ flues running beneath the floors, and the Moors, who adopt stoves visible to the bathers.

Theoretically, radiant heat in a bath is vastly superior to that which is transmitted to the body through the medium of the air. Its virtues have been extolled by David Urquhart and other eminent authorities on the bath. "There is a difference," says Mr. Urquhart, "between radiating and transmitted caloric.... I cannot pretend to treat of this great secret of nature; to work out this problem a Liebig is required. This I can say, that such heat is more endurable than common heat. There is a liveliness about it which transmitted heat lacks. You are conscious of an electrical action. It is to transmitted heat what champagne is to flat beer.... Let us drop, if you please, the word 'bath': it is 'heat.' Let us away with that absurdity 'hot-air': it is the application of heat to the human frame." Elsewhere this writer has pointed out that the terms thermÆ, sÈjac, and hammÂm—the names given to the bath by the Romans, Moors, and Orientals proper—mean heat, and not "hot-air" or "hot-air bath."

My own studies, observations, and experience lead me to the conclusion that the direction in which we shall improve the "Turkish bath" will be in the way of providing sudatories that shall give off pure, radiant heat in such a manner that the whole surface of the body may be sensible of a degree of heat, while the lungs may breathe comparatively cool air—air that has not passed over the sides of a fiery furnace and been suddenly raised to an enormous temperature, but which has received its heat by a gentle and gradual process of warming. Under this system the heat of which we are sensible is as the gentle Zephyr to rude Boreas or the biting eastern winds. If we go into a kiln of brickwork, such as is employed in firing clay goods, after the charge has been removed and all fumes and odours have disappeared, we shall note the soft and balmy nature of the heat that radiates directly from the walls and vaulting. We are, to all practical intents and purposes, in a Roman laconicum. The thick walls have been highly charged with caloric during the firing of the bricks or other articles. They have absorbed vast quantities of heat, and are now giving off the same to the enclosed air and to ourselves standing within. In the old Roman bath the walls were charged with caloric by means of innumerable earthen tubes lining the sides of the laconicum, and covered with a peculiar plaster. But in both cases the nature of the resultant heat is identical. It radiates to one from all sides. There is no acrid biting of the face such as one feels in the worst type of hot-air baths; no unpleasant fulness or aching of the head; and no panting or palpitating. Such is the "bath" of pure radiant heat, a thing totally distinct from, and altogether of a different genus to, the bath of heated air. And one might be pardoned for the enthusiasm which would lead one to suggest that it is only in the supplying of this kind of radiant heat in the modern bath that true and rapid progress can be expected, and possibly that not until this great or partial—according as the system of radiation and convection pertains in existing baths—revolution has been effected, will the bath, at present used by the few, become the custom of the many. Some day, peradventure, this hypothetical method of employing pure radiant heat may be rendered possible and practicable, and we may be placed in a bath where we shall receive great heat whilst breathing a comparatively cool atmosphere, and thus receive a measure of that electrical invigoration we experience when, in some sheltered bathing cove, we have exposed our bodies to the fiercest rays of the morning sun whilst yet we breathe the fresh, cool, ozone-laden air.

Till modern invention, however, has provided us with this desideratum in the heating of the bath, we must be satisfied with existing methods. And unless something really practical is perfected, it is far wiser to rely upon the system of heating by convection through the air—the principle, generally adopted, of continuously passing large quantities of freshly-heated air through the sudatory chambers; exposing, however, the heating apparatus, so that a maximum of radiant heat may be obtained; and carefully guarding against injuring the air whilst raising its temperature. If only existing baths were in perfect harmony with this principle, one would have little cause for complaint, and might the more leisurely await the perfecting of the true radiating principle of heating, which I am satisfied is the one upon which we must base all our hopes for the future of the "Turkish" bath.

For practical purposes, it will suffice if the method of heating and ventilating a bath on the hot-air principle be explained. This I shall now do, and subsequently give plans and instructions for methods of heating and ventilating on systems where, by the exposure of the heating surfaces of furnaces, a large proportion of radiant heat is thrown into the hot-rooms.

The necessary appliances, and arrangements for the heating and ventilation of a bath on the ordinary hot-air principle comprise a furnace in its chamber, with flues or shafts supplying cold, and drawing off the heated air, and a stokery with provisions for firing and storing coke, &c. Too often the stokery is unscrupulously cramped, and the life of the stoker thereby rendered anything but pleasant. Its design is a simple matter, and perhaps for this reason neglected. The arrangement and construction of the furnace chamber requires care, and the selection of a stove or furnace great judgment. As regards the latter feature, the most important point to consider is the nature of the heating or radiating surfaces. What will raise the air to the required temperature, without in the process depriving it in any way of its vitalising elements, and without adulterating it with either smoke and fumes from leakage, or with particles of foreign matter given off from the material employed in its construction?

There is nothing really better as a radiating surface than ordinary firebrick. From this material a soft heat is given off, differing in quality from that obtained from iron. An iron furnace, however, requires less thought in design, gives less trouble in fitting up, and is cheap, economical, and expeditious. Stoves, therefore, with an iron radiating surface, have been largely adopted in the past, in spite of the objection that, when super-heated, particles of metal are thrown into the air of the hot rooms. Of iron furnaces there are many placed before the public; but though all are doubtless suited to ordinary requirements, there are few that are capable of creditably fulfilling the conditions indispensable for the hygienic heating of the air of a Turkish bath.

These conditions may be summarised as follows:—

1. A maximum of heating-surface, with a minimum of grate space.

2. Perfect immunity from the danger of leakage from the furnace into the hot-air chamber or conduit.

3. Freedom from the defect of liability to overheat the air.

4. Inability to adulterate the air by throwing off matter from the heating surfaces.

Such primary essentials must be constantly borne in mind by the designer of furnaces for the Turkish bath. Their importance must be obvious to all.

Of the many iron stoves, Messrs. Constantine's "Convoluted" stove has been adopted the most frequently, as an eminently practical furnace for the effective heating of the sudatory chambers. The appearance of this stove is familiar to all architects, and it will be unnecessary, in these pages, to minutely describe its construction.

The method of constructing a furnace suitable for a small public bath is, however, shown at Fig. 6. The excavations for stokery and heating chamber being completed, and the position of the furnace determined a solid foundation of concrete must be prepared, upon which the brickwork to support the stove must be laid. At the same time, the foundations for walls of furnace chamber, stokery, coke store, and the side walls for the horizontal cold-air conducting flues will be prepared. These latter must then be built in half-brick with glazed interior face, and the furnace inclosed in similar work, as shown in perspective sketch. The flues must be covered with York stone slabs 3 in. thick, up to within three inches or so of the convolutions of the stove, at which distance the side walls of the furnace must be erected, the back one similarly, and the front one round the four projecting doors, which are, respectively, the ash-pit door, the fire door, and two doors for cleansing the horizontal smoke-box and interior of convolutions. The furnace walls must be continued up to a few inches above the bend of iron smoke flue, and then—if, as shown, the furnace be small—covered with a 4-in. York slab in one piece. If the furnace be large, a flat brick arch must form the covering, as at Fig. 8, where this arch supports the flooring of the laconicum. The openings for the admission of the heated air into the conduit leading into the hot rooms may be either directly above, as shown in the last-named illustration, or in the side, as in Fig. 6, with inclined flues. As a rule, it is more economical, in heating on the principle now under consideration, to place the furnace below the level of the hot rooms; but if desirable to place both on one level, the back wall of the furnace chamber becomes the party wall of the laconicum, and it must be stopped short of the ceiling, and the air debouched over it.

In cheap baths the interior face of furnace chamber may be of stock brickwork; but best glazed work should be adopted in good ones. All hot and cold-air ducts should be similarly lined with glazed ware. In first-class work the floors of horizontal and inclined flues should be of white glazed tiles set in cement. Manholes must be provided for cleaning when necessary. Every portion of furnace chamber, flues, shafts, and conduits for hot and cold air must be "get-at-able" either by means of manholes or by long brushes. Air-tight doors must be indicated on the plans wherever this necessity demands them.

The iron smoke-pipe from furnace must be conducted to the smoke flue, and the connection between furnace chamber and flue hermetically sealed. The walls for a small furnace chamber need not be more than 4½ in. thick. Large furnaces require walls one-brick thick.

The cold-air flues leading from either side of the furnace must be conducted to their respective inlets. If possible, at least two inlets should be provided, facing different ways: this with regard to the possibility of certain winds drawing the air out where it is wanted to enter. The openings should be vertical, like windows, and, in cities, furnished with a solid frame and casement, fitted with louvres of plate glass with polished edges. Between the rebate and the casement it is a good plan to leave a space of an inch and a half for a movable stretcher-frame holding several layers of "cheese-cloth" to filter the air. The construction of such an air filter is shown at Fig. 7. The glass louvres keep out the wet, and throw off coarse particles of falling soot; and the provision of a movable stretcher permits the cloths to be frequently changed for clean ones—a very important point, though little heeded, if not, perhaps, wholly ignored.

The position of air intake is a matter of great importance, especially in large towns. It evidently is bad to draw a supply of air from the bottom of an area. Even the position shown in Fig. 8 is not good: the shaft should be carried higher. The best places for the intakes are where there is always a current of pure air blowing, and away from smoky chimneys. Theoretically, it would seem that the higher the level of intake the better; but in cities, by going high we get among the belching chimney-tops, even if we escape the stagnation below. Moreover, a high inlet with a strong wind tending to exhaust the air in the shaft might find the architect with the cold air sweeping through his bath, and all the heated air rushing up the supply-shaft. A large "lobster-back" automatically turning towards the wind, would in many cases prevent such a disastrous result. Even in low-level intakes, as I have said, trouble will sometimes arise from the same cause. This may be remedied by providing more than one inlet, so that only the one facing the current of air will be employed, the other being closed, which could be effected by fixing the glass louvres, spoken of above, on pivots, and connecting them with a rod and adjustable rack. It would be a very simple matter to make the wind itself automatically open and shut the louvres.

The theory of the heating and ventilation of the hot rooms requires most careful study, and the particular scheme to be adopted in any new bath must be well considered with respect to the restrictions of the site. At Fig. 8, I have endeavoured to show how to make the best of what is perhaps a bad job: the site only admits of ventilation at a back area, it is impossible to construct flues anywhere else, and the fresh air must be drawn from the same area. On the ground floor are cooling and dressing rooms; the bath rooms are in the basement and the furnace in a sub-basement, reached from a passage at the end of the stairs for the bather. Two convoluted stoves are shown in a vault; three air-inlets are provided, and the foul air is drawn up into the smoke flues, two in number, which, above, could join one another. Let us follow the air in its passage through the bath. Entering at the intakes, any coarse impurities are thrown off by the smooth louvres, and the tendency of finer particles to rush in is checked by the stretched canvas cheese-cloths. Thus deprived of its actually visible impurities, the air passes through a longer or shorter conduit of glazed brickwork until it reaches the horizontal flues running to beneath the furnace walls, along which it is rapidly drawn, and, ascending between the walls and heating surfaces and between the two adjacent heating surfaces, absorbs the radiating heat and enters the laconicum by way of the rectangular shaft constructed above the vault spanning the two stoves.

Questions of temperature I will omit for the present. The air, on passing through the laconicum, will be practically pure, as it is in such great bulk compared with the number of occupants of this highly-heated chamber, and it will not be absolutely necessary to provide ventilators. These should commence in the calidarium, and should, in the scheme of ventilation here considered, be so disposed that the nearer they are to the lavatorium and shampooing-room, the more frequent will they become. The object of this disposition of outlets for vitiated air is, that the cross currents thus created may not interfere with the main flow from the heating chamber to the lavatorium. Were too many ventilators to be placed near the hotter end of the sudatorium, this stream would be diverted. Too much of the freshly-heated air would flow out at these points, and the onward movement of the air would be enfeebled. There would then be difficulty in maintaining the temperature in the tepidarium and lavatorium.

In passing onward through the various rooms, two changes are wrought in the air: it loses so much of the caloric with which it is charged for every foot it travels, and it becomes laden with the exhalations from the lungs of the bathers. A large proportion of carbonic acid is thrown into the air, and as the normal temperature of the human body remains, in a healthy person, at about 98° Fahr., and rises but a few points even when submitted to the action of heat, these exhalations, in addition to being heavier than air, are very much below the average temperature of a sudatory chamber. Consequently they fall, and must be extracted at the floor level.

The total area of the outlets for vitiated air should be about equal to the area of the narrowest part of the shaft that conducts the fresh, hot air from the heating chamber. Thus, supposing the latter to be 5 superficial feet, and the size of outlet ventilators a clear 12 in. by 3 in., there may be 20 ventilators disposed round the bath-rooms, say 4 in the calidarium, 7 in the tepidarium, and 9 in the combined shampooing room and lavatorium.

In the diagrams at Figs. 8 and 9 the foul-air conduit is the space comprised under the marble-topped benches running round the hot rooms. At the end of the laconicum they enter flues, which I have shown as running side by side with the smoke flues.

Other methods of heating the air, besides those mentioned, include coils of iron flue-pipes in a brick chamber—a principle that has been frequently adopted in the past—and plain cylindrical iron radiating stoves, such as employed at the Hammam in Jermyn Street.

In the latter plan, however, a great expense is created by the large number of furnace-fires to be kept constantly burning. An exposed stove in a hot room, has, moreover, the objection to its use that it re-heats the air in the bath, which should never on any account be done.

If the iron stove-pipe system is adopted, a furnace similar to the one shown at Fig. 10 must be provided, and after an additional few feet of brick flue the iron pipe would commence and turn back upon itself much as the flue in the fire-brick furnace. Proper supports must be provided, and the pipes must be stout and jointed together with expansion joints, otherwise considerable difficulty will be found in keeping a long length of flue pipe perfectly free from leakage. Furnaces on this principle may be designed so that they throw a certain amount of radiant heat direct into the hot-rooms, and they possess this advantage over a mere stove, that they warm the air more gradually. The furnace should be built adjoining the laconicum, the partition wall being of 4½-inch glazed brickwork, having a large number of small openings made therein by leaving void spaces as described further on for the fireclay heating apparatus. Behind this wall the iron flue-pipe should be placed, turning back upon itself, as described above, for perhaps half-a-dozen times, and ending in the vertical brick flue. The furnace itself should be of fire-clay, and so designed that its utmost heating power may be economically employed in warming the incoming air, which should pass over the furnace and iron flues, through the holes in partition wall, and thus into the hot rooms. The flue, if of wrought iron, should be rectangular in section, but if of cast-iron it should be round.

The most economical way of obtaining a high temperature in a small, inexpensive, and unpretentious private bath is by means of a common laundry stove, with a longer or shorter length of iron flue in the apartment. This is the cheapest and quickest method of raising the temperature of a room for sudorific purposes.

To turn to methods of heating from a radiating surface of firebrick, at Fig. 10 I have given the plan, elevation, and sections of a fireclay heating apparatus. It is constructed wholly of fireclay—fireclay bricks, quarries, and cement. In the main it consists of a long flue of firebricks and slabs, which coils backwards and forwards over itself till the desired amount of radiating surface is gained. Between the coils are spaces for super-heating the air already warmed by passing over the actual furnace and into the warm air chamber, the air passing through by means of perforated bricks. The illustration shows a simple furnace; but it would be an easy matter to improve upon this by providing iron air-tight doors lined with fireclay, for cleansing flues and air-chambers. The example given is only suited to heat a small public bath. For a large set of hot rooms, a compound apparatus could be constructed by placing an additional furnace in a sub-basement, the one on the level of the sudatory supplying radiant heat, and the lower one hot air. Two such apparatus might be placed one behind the other, end to end, or might form the sides of the laconicum; the last plan, however, being the least to be recommended, as in such positions they would not directly radiate their heat into the adjoining hot rooms.

The advantage of such a furnace as that shown is that it supplies radiant heat of a most exhilarating kind, besides a proportion of heated air, and from a fireclay surface, the employment of which renders it absolutely impossible to overheat the air, or to contaminate it by deleterious particles resulting from the decomposition of metal. Moreover, the stoking of this class of furnace requires less arduous attention than an iron stove. Its disadvantage is that, should the temperature of the bath be allowed to fall markedly, it requires some time for the extra heat to be made up again. Inasmuch, however, as fires at public baths must be kept banked up overnight, this is not a matter of importance. It is this very slowness of increase in temperature that constitutes the safeguard against that overheated air, the presence of which we can, with practice, detect by the smell in so many baths. The difficulties involved in the construction of a furnace of this nature relate to the prevention of cracking and consequent escape of sulphurous fumes and carbon into the air. The very simplicity of the construction of the flues and air-chambers constitutes the chief danger, as the chances are that, unless the architect stands by and sees every joint made, the work will be done badly. Absolutely faultless workmanship must be employed throughout, and the fireclay materials must be literally of the very best and soundest description. Every single joint must be perfectly made with fireclay cement or paste. The fireclay bricks, &c., must be selected with regard to the amount of indestructible silica in the clay, consistent with hardness and toughness. Homogeneity of material must be obtained, having regard to expansion and contraction. The same material used for the bricks, &c., worked into a paste, must be employed for the joints.

The design for a furnace on the principle shown at Fig. 10 must be prepared with constant regard to expansion and contraction in heating and cooling. Should this warning be disregarded, fractures will result. It will be seen, upon reference to the plans, that the block of flues and air spaces is left quite free, to allow of any expansion, the connection with the smoke-shaft being by means of an iron flue-pipe, which, being provided in considerable length before passing through the party-wall of laconicum and stokery, by its flexible nature permits any slight movement in a vertical direction. If an "expansion" joint were provided, there would be a sufficient length of iron pipe if it passed direct from the junction with the heating apparatus into the stokery. So much of the iron flue as is in the laconicum must be coated with asbestos or some composition, or the heating will not be wholly by firebrick. The junction of iron flue and heating apparatus is shown by a cast-iron cap sliding over a projecting rim of fireclay, moulded into the last quarry cover, similar to the way in which cast-iron mouthpieces are fitted to retorts.

This heating apparatus is shown visible in the laconicum, but if thought desirable it could be screened by a wall of glazed bricks—9 in. and miss 4½ in. The 4½ by 3 in. holes can be arranged in diamond patterns. This screen wall, however, cuts off a large quantity of radiant heat.

The first flue past the actual furnace—shown with ordinary dead-plate, raking fire-bars, ashpit, fire-door, and ashpit door for regulating draught—has walls 4½ in. thick; above, smaller bricks, 3 in. wide; but in a larger apparatus, 9 in. and 4½ in. respectively would be required. The quarries between flues and air spaces are 24 in. by 24 in. by 3 in., with rebated joints. Larger covers would be more liable to crack at any provocation.

In addition to heating by means of furnaces, steam-heating may be employed, if found, as in many cases it would be, convenient and economical. The chief disadvantage of this method of heating Turkish baths, is the constant danger, however slight, of bursting a pipe in the heating coil, which, by immediately filling the highly-heated atmosphere with vapour, might prove most disastrous to the occupants of the hot rooms, who would be seriously scalded. Nevertheless, the principle has been largely employed in the heating of the most recent Turkish baths in Germany.

If adopted it may be either on the hot-air or radiating plan, as in heating by means of furnaces. In the first method the fresh air is introduced into a chamber containing a coil of steam-pipes, and passes thence into the laconicum by a shaft or conduit, as in the case of air heated by a stove. In the second method, steam radiators—compact batteries of pipes—must be placed in recesses in the hot rooms, fresh air being introduced over them. The steam-pipes employed should be of the "small bore" type, about 5/8 inch internal diameter, and of wrought iron or copper. In order to ensure as far as possible against the danger of explosion, the system of pipes should be tested, when fixed, by severe hydraulic pressure.

It is certainly a great advantage, in point of ease and economy, to be able to warm a building, drive machinery, and heat Turkish and Russian baths from one boiler, which can readily be done, very ordinary pressures of steam giving sufficient heat to keep the radiators of the requisite temperature. But the nature of the heating accomplished by means of steam-pipes is very inferior to that from large radiating surfaces of firebrick.

The average temperatures of a public bath should range from about 110° in the shampooing rooms to 250°-260° in the hottest part of the laconicum, taking the readings of the thermometer at a level of 6 ft. 6 in. above floor-line. Between the entrance of the heated air and its point of furthest travel in the shampooing rooms, the bather should be able to select any temperature that may be most agreeable to him, and as many find by experience that a certain degree of heat is best suited to themselves, it shows attention to the habituÉs of the bath, if the hot rooms are carefully maintained at the same uniform temperatures throughout the year. This may be 110°-120° in the shampooing rooms, 140° in the tepidarium, 180° in the calidarium, and 250° in the laconicum. These must be the maxima of the average temperatures of each room at 6 ft. 6 in. above the floor. In a pure atmosphere the highest temperatures are comfortable, but in a foul one they become insupportable.

In a good bath, where there is a rapid and continuous flow of air, there will be comparatively little difference between the temperature at say 4 ft., 6 ft., and 8 ft. above the floor. In badly-ventilated rooms, where the air stagnates, there will be a considerable difference. And here we may note a serious objection to the heating of a bath by convection; for while the head may be in a high degree of heat the feet are in comparatively cool air, whereas, if possible, it should be just the reverse. In convected heat, this of course applies in its entirety, as where so-called radiant heat is employed the evil is not quite so marked. And here, too, we may note the admirable nature of the Roman system of heating, where the floors radiated the majority of the heat, and the walls a slightly less amount. The fresh air under the ancient system must have entered through the cooler rooms, and being drawn towards the calidarium found its exit through the ceilings, at times by way of the regulating device mentioned by Vitruvius. Thus the ancient bather would not suffer the inconvenience that accrues to the bather in the modern hot-air bath, whose head, when he is standing upright, is in a considerably higher temperature than any other portion of his body.

The temperature of a bath should not be regulated by the firing of the furnace. This should be regularly stoked, and kept at one uniform heat-giving condition. Bad firing and forced firing may crack the stove should it be of iron, and the air may be overheated. The temperature should be regulated by means of the hit-and-miss ventilators at the floor level. Fanlights between the various hot rooms, with screw-rod adjustment, serve as a means for regulating their relative temperatures.

The heating power of furnaces must be studied. Having calculated the cubical contents of the rooms to be heated, and given the heating power of the stove or apparatus to be employed per cwt. of metal or superficial foot of radiating surface, we arrive at the necessary size.

Messrs. Constantine give the following tables to show the heating power of the "Convoluted" stove. The figures give the requisite size of stove to raise the air to about the relative temperatures I have mentioned before, and with ordinary firing.

When different kinds of heating apparatus are employed, their heating power must be carefully ascertained and calculations entered into, or it may be found necessary to resort to the costly and humiliating process of dragging out the stove or pulling down the furnace and refitting a larger one. This point is worth attention. Such mistakes are not unfrequently made.

As regards the amount of air that should flow through the hot rooms, an allowance of 40 cubic feet per head per minute should be the minimum, if purity of atmosphere is to be maintained. In a bath, the importance of perfect ventilation cannot possibly be over estimated, as not only has the respired air from the lungs to be removed, but also the deleterious exhalations from the skin which are produced by perspiration.

The allowance of 40 cubic feet per head per minute should not, if properly distributed, cause an unpleasant draught in any part of the hot rooms; for it must be remembered that even in a highly-heated atmosphere a waft of air of the same temperature is felt to be cold. The main thing to be studied in this provision of a large volume of air is that the cold inlet be ample, and the passage from this intake to the point where the air is debouched into the laconicum equally roomy and unobstructed. The rapidity of flow will depend upon the means provided for the extraction of the foul air. With large horizontal flues, and a capacious and tall shaft, the so-called natural system of ventilation will be as effective as could be desired. Greater extraction power is gained if in the brick stack a smoke-pipe can be placed running up the whole height. In many cases mechanical ventilation could be employed with the greatest benefit. A powerful air-propeller fixed at the end of a system of horizontal flues under the floors of the hot rooms, and running so as to exhaust, would do away with all the objectionable odours and nastiness of many baths.

The purity or foulness of the air in the hot rooms forms all the difference between a good bath and a bad one, which latter is infinitely worse than no bath at all. There exist, at the present time, scores of baths where the odours of the sudatory chambers are nauseating. Such foulness arises from stagnation of the air. There is no continuous flow, and the respirations and exhalations of the bathers are not removed. A system of ventilation may be pointed out, but it is on the wrong principle, and does not act. There is no change of air. The atmosphere of such places becomes pestilential.

Owing to the expansion by heat, a relatively greater volume of air enters the laconicum than the cold intake. This fact, however, does not practically affect the arrangements for ventilation, &c. Theoretically, however, it would seem to demand that the shaft conducting from furnace to hot rooms should be of greater sectional area than that to the furnace from the intake—about one-third larger—and that the total area of outlets for the escape of vitiated air should be about midway between the two.

The whole principle of the ventilation of the hot rooms of a Turkish bath resolves itself, primarily, into the fact that we have to continually remove the bottom layer of air. The provision of the foul-air conduits below the floor level is equivalent to providing a suspended floor with a hollow space under. This is just the reverse of the principle of ventilating rooms of ordinary temperature, where we require to constantly remove the top layer, and often actually do so when we provide false ceilings to passages, &c.

The ventilators placed at the floor level of the hot rooms should be actually so, and not 3 in. or 6 in. above. Long, wide gratings 6 in. deep are preferable to those of deeper and narrower design. In theory, indeed, the whole circumference of the hot rooms should be lined round with gratings, thus making the sudatorium like a lidless box inverted, into which hot air is thrown and escapes all round the bottom edges.

There is one point about the circulation of air in a set of hot rooms that requires considerable attention, and that is the back-flow along the floor. In any bath where hot air is supplied, if the bather will hold his linen "check" across the top of the doorway between the rooms he will find that the air is flowing from the laconicum to the shampooing room. If, however, the sheet be held across the lower portion of the doorway, he will find that there is a current of air setting in an opposite direction—from the shampooing room to the laconicum. This is shown at Fig. 11.

It will be seen from the diagram that the bather is really in this back-flow when he is standing between and in a line with the doors of the hot rooms. All the air appears to be travelling along the top of the bath, and the bather reclining on the marble-topped benches would seem to be bathed in air that has passed along the top of the bath, round the shampooing rooms, and back along the floor. In reality, however, it is only from door to door that the currents exist exactly as shown at the diagram, Fig. 11, there being a secondary circulating process in each room.

This circulation of air will exist in any bath heated on the modern system—that is to say, where freshly-heated air is passed in in sufficient quantity. It is a natural result, and tends to distribute the heat more equally. The back-flow is only objectionable when a door is opened direct from the heated shampooing rooms to a cooler apartment, as the plunge bath chamber. The bather standing in a line between the doorways may then feel a cold draught. To guard against this, double doors, with a small lobby between, should be provided to any means of communication with a cold chamber.

A set of hot rooms could be constructed so that the bather would be in the top current of air that flows from the heating apparatus. By reference to Fig. 11 the reader will understand that by the provision of a platform or grating midway between the floor and ceiling this end would be attained.

The atmosphere of the sudatorium must be perfectly free from vapour. "Perfect dryness of the air," says Mr. Urquhart, "is indispensable to the enduring of a high temperature.... This dryness is further requisite for electrical isolation. With vapour in the chamber an atmosphere is created injurious to health and conducive to disease. It is the very condition in which low, putrid, and typhus fevers flourish. The electrical spark will not ignite in such an atmosphere, and the magnet will lose its attractive power. We all know the difference of our own sensations on a dry and on a damp day."