railroad-stations, for markets, and for large buildings such as those for exhibitions. These immense buildings, covered in most cases with glass roofs, which often leave only a very small space for the escape of the smoke and steam of the locomotives and of the hot air in summer, sometimes become unendurable for the employés. One end of the building is almost entirely shut in by the gable-wall containing the main entrance; the other usually has an opening only high enough for the passage of the locomotive; the sides occupied on the ground-level by waiting-rooms, &c., and on the second and third floors by offices, do not allow the air to have access to the building, and in the hot season the temperature rises near the ground-level to 104°, 113° and even 1220, as has been observed at the stations of the Lyons, Eastern, and Strasburg railroads. In order to remedy this state of things, it is necessary to raise the skylights on the roof, not only because they are too low, but because in winter they cool the smoke and partially condense the escape-steam of the engine, and thus interfere with its removal. Instead of placing the sky-lights at the ridge of the roof, it would seem better to place them near the eaves, making them, as at present, equal to one-fourth or one-third the total surface. The ventilating-opening should be formed by two vertical walls of sheet-iron about 10 feet high, leaving between them a passage extending the whole length of the roof, the breadth of which should be calcu lated so as to renew the air of the station at least twice or three times an hour, on the supposition that the heat of the sun in summer is sufficient to produce, in a sheet-iron chimney 10 feet high, a velocity of from 1 to 2 feet a second. To replace regularly the air removed without producing unpleasant currents at the end-openings of the station, it is necessary to increase the number of openings for admission of air, and place them as uniformly as possible throughout the extent of the station, and also to make large doorways in the two ends of the building. The total area of the freshair openings should be such that, with a velocity of at most 16 to 20 inches a second, a volume of air may enter into the station equal to twice or three times its cubical capacity. 98. Sprinkling of roofs.-In addition to the preceding arrangements, proper for all seasons, it would be well, in hot weather, to keep up a constant sprinkling of the roof, commencing at seven or eight o'clock in the morning and lasting till five o'clock in the evening, using about 4 cubic feet of water an hour to every 100 square feet of roof-surface. This sprinkling, which will be sufficient to prevent the heating of the roof by the action of the solar rays, added to the continued aeration, will maintain the temperature within convenient limits during the hot season. 99. Example.-The Orleans station is 348 feet long, 92 feet wide, 26 feet high at the springing-line, and 44 feet to the ridge. Its cubical content is about 1,130,000 cubic feet. 3 × 1130000 3600 To renew the air three times an hour, it should carry off=942 cubic feet a second. The velocity which the solar heat may give to the escaping air being estimated at but 1g feet a second, the sectional area of the ventilating-space should be 574 square feet; and if the ventilatingpassage is carried the whole length of the roof, which is 328 feet, it would suffice to make it 1 foot 9 inches wide. But as the part where there is most smoke and steam is usually near the end at which the trains leave, instead of making the ventilating-opening extend the whole length of the station, it would be better to give it greater breadth and less length, still retaining the same sectional area. COURTS AND COVERED MARKETS. 100. Similar arrangements should be adopted in the case of courts and for all covered markets. In the latter, where blinds are usually placed in the windows, the introduction of air is easily provided for, and it is particularly the removal of foul air that requires attention. GLASS ROOFS AND CEILINGS. 101. Influence of glazed roofs and ceilings during the winter.—If in the summer season the glazed roofs of stations and covered courts present the inconvenience of producing a heating effect, which it is necessary to overcome, in winter they have the contrary defect, which often leads to very disagreeable results. The conductibility of thin glass then leads to a considerable cooling of the interior layers of air in contact with the glass; this air, becoming denser than that below, descends, and is constantly replaced by more, which is likewise cooled, and by this continued movement the rooms thus covered become very difficult to warm. To these troubles is added that of the motion of the cold air, which naturally flows toward the chimneys, or the discharge-openings, if there are any, so that the occupants feel a descending current of cold air, the more unpleasant the nearer they are to the chimney or the dischargeopenings. If the glass roof is simple, and has, as is almost inevitably the case, joints, through which the external air-much colder than that in contact with the internal surface-penetrates into the room, the effects which have been mentioned become more sensible and disagreeable. There is also the danger that water will enter during rain-storms. It is, then, necessary in occupied buildings, when similar plans are adopted for lighting, to place under the roof a glass ceiling with as few joints as possible, and in the loft thus formed and limited above and below, to provide heating arrangements which will prevent the cooling of the ceiling, and thus to avoid the cold air currents which have just been referred to. 102. Observations at Château de Ferrières.-The most striking example of these effects which I have had occasion to observe is presented by the great reception-hall of the Château de Ferrières, and it has furnished me with some facts which enable me to determine the amount of heat which such glass roofs may transmit, and, consequently, to determine approximately the methods of heating to be employed to prevent this cooling. The main reception-room of the Château de Ferrières, called the Hall, is 75 feet long and 40 feet wide, or 3,000 square feet in area. It is completely surrounded by other reception-rooms, corridors, vestibules, &c. By means of heaters, all these are comfortably warmed, as well as the reception room, which has no side-windows, but is lighted by a glass ceiling with a surface of 1,635 square feet, covered by a glass roof in seven sections, having together 2,459 square feet of cooling surface. A large fire-place, in the form of a monument, placed on one of the long sides of the room, completes its system of heating. When in winter the space between the glass roof and ceiling is not warmed during the day, the effects previously mentioned become the most unpleasant. The considerable draught of air produced by the fireplace draws to it the air cooled by contact with the ceiling; and the vicinity of this fire-place, to which persons are naturally drawn by a bright fire, becomes unendurable. At night, the room is lighted up by 1,000 gas-burners above the ceil ing, which consume 3,500 cubic feet of gas an hour; there being then about one burner to every three square feet of floor-surface in the room. The heat given out by this abundant combustion more than suffices to prevent the cooling of the air of the room and the unpleasant effects which would result from it. To obtain at least to a certain degree the same result during the day, it has been found necessary to keep up coke-fires in four cast-iron stoves, placed in the roof-space, in order to maintain there a temperature higher than that of the room. Observations made on the consumption of coke during the day and of gas at night, as well as upon the internal and external temperatures, enable us to calculate at least approximately the amount of heat required in the space between the glass roof and ceiling in order to prevent the unpleasant cooling effect. For this purpose, calling C the number of units of heat which can pass in an hour through a pane of glass having the surface S; T the temperature of the air on the warmer side; T' that of the air on the colder side; K a constant co-efficient, representing the number of units of heat to a square foot of glass surface, and to a degree of difference of temperature between the two faces: The amount of heat passing in an hour through a glass ceiling or roof will be given by the formula C=KS(T- T') Engineers only admit for the co-efficient K the value K = 1, while the data obtained at Ferrières seem to show that for a double glass covering that is to say, a glass roof and a glass ceiling-it should have the value K = 3, and for a single covering K = 4, especially as in the latter case cold air might penetrate into the interior through the joints of the glass. According to these values, allowing that the developed surface S' of the roof is one and a half times that of the glass ceiling S, the amount of coal to be burned in the coldest weather may be calculated as follows: Let The temperature of the external air be 14°; The temperature to be maintained within the roof be 1130; The amount of heat passing off through the glass roof will be— The amount of heat passing off through the glass ceiling C = 3 × 1000 (113 — 59) = The amount of heat to be developed within the double roof= 445, 500 units. 162, 000 units. 607,500 units. Admitting that the coke-stoves employed utilize, as is almost always the case under similar circumstances, 90 per cent. of the heat given out by the fuel, and that a pound of coke produces 12,600 units of heat, it is necessary 607500 to burn every hour =53.57 pounds of coke an hour to prevent, .90 × 12600 under these almost extreme conditions of cold in Paris, the glass from cooling the room beyond 59°. At evening-receptions, the lighting-up of the room requiring a burner consuming 34 cubic feet of gas an hour to every three square feet of floor-area, the heat produced will always be more than sufficient to prevent the cooling of the interior. The preceding figures show why most makers of heating-apparatus who have undertaken to warm halls or courts covered by sky-lights have only very imperfectly succeeded. DWELLING-HOUSES. 103. Among the appendages of dwelling-houses which most often give out disagreeable smells should be placed, in the first rank, yards, kitchens, and privies. In consequence of the draught exerted by the chimneys of rooms near these places, it often happens that at certain times more or less infectious air is drawn into the apartments. To avoid this serious trouble, it is necessary, by means of proper arrangements, which should also be simple, to produce a regular and almost constant motion of air from the apartments or the halls toward these places, discharging from them to the exterior. This may be accomplished in several ways. 104. Court-yards of dwelling-houses.-Apartment-houses, especially in Paris, very often contain little yards, belonging to the stores on the ground-floor, which seriously affect the healthfulness of the upper stories. Provision-stores, restaurants, dye-houses, drug-stores, &c., give rise to disagreeable or injurious smells, which rise and annoy the occupants of the house and injure the property. These disagreeable effects may easily be overcome in the following way: The yard should be covered, in whole or in part, with a glass roof, forming a single inclined plane between the ground-floor and the second story. In an angle, and at the upper part of this roof, should be placed a chimney, extending above the upper cornice, the section of which should be calculated so that with a velocity of about three feet a second the air of the court-yard will be renewed once, or, better, twice an hour. At the lower part of this chimney should be placed a gas-burner, consuming only 34 cubic feet an hour. The velocity being small and the chimney high, about 1,800 or 2,000 cubic feet of air may be carried off in an hour by this chimney to every cubic foot of gas burned, and thus a constant purification of the yards be secured. When local arrangements favor, it will only be necessary, in order to keep up the draught, to carry a smoke-pipe up the chimney, or to start a fire in a coke-stove placed in it. 105. Kitchens.—When ranges with hot-air passages, such as are now in general use, are employed, it will be easy when they are put up to place hot-water pipes around the grate, and carry them a certain distance up the chimney and back to the range, as in the boilers of hot-water heating-apparatus, which would secure a sufficient draught. 106. Use of gas-burners for the ventilation of kitchens-In kitchens lighted by gas, when the ranges are already put up in the usual way, lighting one or two gas-burners at the bottom of the chimney, to be kept burning only while cooking is going on, would in most cases suffice to produce a draught sufficient to carry off all smell. Example. The kitchen for a single flat in Paris is considered quite large if 10 feet long, 13 feet wide, and 113 feet high; that is, with a content of 1,490 cubic feet. It follows from direct experiment that, with the aid of a single gasburner, consuming 14 feet an hour, and kept burning only while the meals are being prepared, that is to say, at most six hours a day, there may be produced every hour, with sheet-iron ventilating-pipes 9 inches in diameter, and |