The best means of warming buildings, and of producing an artificially warm atmosphere in conservatories and forcing houses, has often been the subject of discussion in the columns of the SCIENTIFIC AMERICAN ; and the general testimony has been in favor of heating by means of hot water, the numerous advantages of which it is needless to recapitulate. It may not be out of place, however, to mention that with them the air is never in contact with red hot metal, it cannot by any possibility reach a temperature as high as in the hot air furnace, and it becomes charged with no deleterious gas, but always remains the same in chemical and mechanical characteristics as when it entered the arrangement to be heated. Our illustration is a perspective view of the excellent arrangement for heating air by hot water, invented by J. Brown, of this city, and patented by him May 30, 1854, and re-issued to him August 14, 1855. A portion of the brickwork is removed to show the arrangement of the tubes, and the course of the air and water. A solid brickwork foundation being prepared, the boiler, B, is set therein, the fire door, F, being let into the front of it, and the fire box is made of the boiler itself, so that there is always a mass of water surrounding the fire ; by this means all the heat produced by the combustion of the fuel is made available, and is absorbed by the water. The whole of the apparatus being filled with water, when it gets warm it gradually begins to ascend from the boiler, B, up the rise pipe, R, and from that to the distributing pipe, D, from this the cold water descending the pipes, P, allows the warm water to descend in them also, and come by the return pipe (seen at the bottom of the boiler) into the boiler again ; thus a continuous circulation of warm water gradually becoming hotter, is secured—the arrows in the pipes indicate the direction of the cur- rents. But if the fire is kept up, the water would commence boiling, and stoam be generated, which would totally stop the action of the apparatus. This is prevented by an ingenious device. When the apparatus is full of water, it rises through the pipe, G, up to about an inch in the box, V, which is divided into two compartments up to about four-fifths of its hight, and a siphon connects the two compartments. When ebullition commences, this water is, of course, thrown over the top of the compartment, and passes through the pipe, 5, into the box, e. In this box, e, there is a float, which, as it rises, closes the lower valve, f, of the draught box, E, that admits the air under the fire, and thus supports the combustion, and elevates the upper valve or damper, f, which admits the cold external air on to the top of the fire, and thus checks the fire, and the current of air cools the water in the boiler down to a proper temperature. The external air finds its way to the draught box, E, by means of the pipe, H, which is represented as broken off. a is a pipe by which any steam that may by chance be generated can pass down into the fire, and thence to the chimney. The cold air coming down through flue, C, and space, C, is warmed by contact with the pipes, P, and passes up through the pipes, W, to the registers, or other means of rendering it available for warming the building. The white arrows indicate the direction of the current of air passing in cold and out warm. It will be seen from this description that the air can never become too hot, and the apparatus is self-regulating in all its parts, and compensates for any expansion of the water at the boiling point. A continuous ventilating, as well as warming current of air is secured through the building, and the air is as pure as the moment it entered the flue. Any more information concerning this apparatus can be obtained by addressing Brown's Water Furnace Co., 274 Canal street, three doors east of Broadway, New York.