diminish it when the difference is small, without reference to the absolute height at which the thermometer may stand: hence it necessarily follows, that, if the apertures are calculated to change the air with sufficient rapidity in the heat of summer, when the difference is very slight, they will occasion an enormous waste of heat in the winter, when the difference is very great, by carrying off the air too quickly; or, on the other hand, if calculated for ventilation as required in the winter, they will fail to answer the purpose in the summer. If it be replied, that the equilibrium of the dampers can be occasionally altered, so as to require a greater or less pressure on the lower surface to produce the same effects, it is obvious that the great advantage of the self-regulating principle will be entirely lost. I am quite prepared, however, to admit that the principle is an excellent one, and, could the practical defects I have pointed out be avoided, it would be well worthy of a trial. Perhaps the very best method of ventilating any building where it is requisite to produce an artificial current, is by having a fire in a close chamber in the roof or upper part of the building, the only supply of air to which is procured by means of flues communicating with the different wards or rooms to be ventilated. These flues, which might be furnished with registers or slides to adjust the ventilation, would cause a constant and regular change of atmosphere under all possible circumstances, and at all seasons of the year. This plan, however, would in all cases be expensive, and in many instances impracticable. Probably the next best mode is to let the air admitted be, as nearly as possible, of the temperature which it is desirable to preserve in the apartment; with a sufficient number of apertures, furnished with slides, in such situations in the upper part of the room as may be most convenient, for the exit of the air. When the air in the apartment is warmer than that outside, of course it will have a constant tendency to rise and escape. In the heat of summer, if it is possible to procure a supply of cool air from below ground, and at the same time to heat the air above the room, so as to cause it to rise, it is evident the cooler air will be forced by the atmospheric pressure to supply its place, and a temperature below the average of that outside will be maintained. In a Lock Hospital lately erected by the trustees of the Liverpool Infirmary, designed by myself, and executed under my superintendence, an attempt has been made to combine these advantages, and hitherto with complete success. The wards for patients are rooms about 50 ft. by 20 ft., and 13 ft. 6 in. high, containing about fifteen or sixteen beds in each. There is no basement story, and the vacant space under each floor communicates with the external air by a number of small gratings. Two air-flues in the jambs of each fireplace are open below, and communicate with the back of the grate just above the floor. The grates, of which there are two in each 110 apartment, are registers, with air-chambers running completely round the back and sides, but separated in the middle. Fig. 110. shows the plan of the grate and are the flues on each side jambs, and fig. 111. the front view: aa the fireplace; bb, the air-chambers; and, by a lining of brick inside, the air is made to pass within 3 in. of the heated back and sides of the grate; c c are the slides for the admission of warm air into the apartment. These grates were executed by Messrs. Pooley and Son, of Liverpool. It will be seen, by the plan, that none of the heat at the back and sides of the fire is lost; but, being communicated to the air admitted from below, a fine stream of air, warmed, but not heated unpleasantly, is constantly pouring through the orifices into the room. For the escape of the air, there are six flues provided in each ward, about 14 in. by 9 in. each, built in the walls, and opening at the top into the space between the ceiling and the roof, with two apertures to each flue from the room, one at the top near the ceiling, and the other a little above the floor, each furnished with a slide. For the escape of the air from the space under the roof, pagoda caps, formed of concentric rings of cast iron, about 2 ft. in diameter, are fixed, one on the roof of each ward. If it is required to preserve as much heat as possible in the apartment, by closing the whole of the upper slides, the air being able to escape from the bottom apertures only; the whole mass of air in the room must be heated to one temperature before any can be permitted to escape. In like manner, by opening or closing any portion of the slides for the admission or exit of the air, the temperature and ventilation may be regulated at pleasure. In the summer, the air in the space under the slates, being highly rarefied by the direct action of the sun's rays on the upper surface, is continually passing off through the caps; while the air admitted through the apertures cc, coming from the subterranean space below the floor, is considerably below the temperature outside. In addition to this, the windows can, of course, be opened when requisite; and, being all on one side of the rooms, and a considerable height from the floor, any unpleasant draft is avoided. Of the efficiency of the above plan, I can speak with the utmost confidence; and its simplicity and cheapness will, I think, be evident on inspection. The warmth diffused by the grates is such, that, though two are fixed in each ward, of the size mentioned above, it has never been found necessary to use more than one at a time. Liverpool, April 18. 1834. ART. V. On a Method of preventing the Damp from rising in the Walls of Buildings on Clay and other moist Soils. By WILLIAM J. SHORT, Esq., Surveyor. ON reading Mr. Hawkins's article (p. 123.) on the means of preventing injury to walls, &c., from damp, it has occurred to me that the following method might be employed to prevent the damp from rising in walls, at the same time that it provided ventilation sufficient to keep dry and preserve the timbers of the ground floors. When building the house, I would leave, as the works proceed, a vacancy or channel in the centre of all the walls, as shown at a in fig. 112., laying over the same, slabs of hard 112 cheap stone or slate, which may be chamfered off so as to form a neat finish to the plinth round the outside of the building. At various intervals, I should propose that small openings communicating between this channel and the interior of the building (as shown at b) should be made; so that a current of air from the exterior may be driven through the channel and openings under the floors, in order to sufficiently ventilate the same. The only increased expense will be the difference between a course of stone or slate and a course of bricks; as leaving the vacancy or channel will be, if any thing, a saving. Clapham, May, 1834. ART. VI. On a Method of curing Smoky Chimneys, and of ventilating Rooms. By Mr. SAUL. I HEREWITH send you a sketch of a plan for curing smoky chimneys. It is the invention of Mr. R. Hall of this town, a 113. ART. VII. professed chimney doctor. have seen several rooms where it has been adopted, which have been completely cured of smoking. As the plan is very simple, it may be executed at a trifling expense. A current of air passes over the door behind the architrave or moulding (a a, in fig. 113.); the arrows show the way by which the air enters; and, as it rises direct to the ceiling, a person sitting in the room feels no draught whatever. This plan may be adopted without disfiguring the room in the least, as the architrave is taken off and rounded on the back part, and is then replaced in such a manner that the aperture by which the air enters is not seen. Sulyard Street, Lancaster, On Cast-Iron Angles for Outside Doors. By C. H. I HAVE often thought that outside doors might be greatly improved by having cast-iron angles at the bottom, in the following manner: In fig. 114., a is the upright style; b, the bottom rail; 114 115 c the horizontal section at ef, showing the top of the iron angle foot, and the section of the style. The expense of these angular pieces of cast iron would be about 7s. or 8s. a pair. There would be much saving of labour in making door frames in this manner; and, as the angles of doors constructed wholly of wood are liable to rot, those with cast-iron anglès would have a great advantage over them. The same plan may be applied to posts for parks, &c., by having iron sockets (fig. 115.) made very light, and to fit on to the part to be inserted in the ground. These sockets may, I think, be made at from 3s. 6d. to 4s. each; and, of course, there will be a saving of timber when they are used. Birmingham, June 16 1834. ART. VIII. Dovetailed Caps for Wooden Fences. 66 A DESCRIPTION of a wooden fence which may be put together without the use of nails, screws, or other iron-work, is given in p. 79., in which the inventor states that wooden pins are liable to various objections, and do not make so neat a finish as where nails are used." Now, I shall feel obliged if you or any of your correspondents will point out in what respects wooden pins are either unfit or inelegant for works of this description. I I think Mr. Cottam's dovetail cap is liable to several objections; namely, the expense, and the increased number of grooves and tenons, which, by receiving, and for a long time retaining, moisture, are known to decay in a very few years. A great portion of the rain which would fall on the cap would, by means of the dovetail, be conducted to the ends of the rails, which, together with the dovetail, would shortly be rotten. am of opinion that the end of the dovetail is more unsightly than a wooden pin, though certainly neater than the wedges under the bottom rail, shown in Mr. Cottam's sketch. This method of fastening would not prevent the top of the post from being moved sidewise, as there is nothing to tie the rail firmly to the post. The cap, by swelling and shrinking, as the weather was moist or dry, would soon become loose; and, when cattle (as is frequently the case) rubbed themselves against it, it would fall off, and the rails probably be lifted from their bed and broken. I should suggest the fastening of the upper rail in the manner shown in the accompanying section (fig. 116.), where a is the cap, having one end of a strong wooden pin (c) driven tight into it. The corners of the cap, formed so as to drip the water at four points clear of the rails, are shown at e e; and the rails (dd) are overlaid and fastened in the post (b) by the pin (c). The bot |