Our readers will be prepared, by several articles which have lately appeared in the SCIENTIFIC AMERICAN, upon the subject of fire-proof and rat-proof buildings, to examine critically the device herewith illustrated. The inventor has spent three years in experiment and study to perfect this system, and, while primarily aiming only to perfect a system of fire-proof building, now claims that he has secured several important results not at first contemplated. One of these coincident results is the rendering of a building rat-proof as well as fire-proof. A second is, that a very superior wall to that formed by plastering on wooden lath is obtained ; the cement or plaster not drying out rapidly, but retaining its moisture until a perfect chemical combination has taken place between the materials of which it is composed. The plaster is found, after it has hardened, to be four times as hard as common plastering. Thepeculiar form of the iron laths also prevents the falling down of any portion of the plaster from any ordinary cause, or from the action of great heat. Great pains have been taken to bring the cost of this method down to such a figure that it can successfully compete with the ordinary materials and methods of building. The inventor informs us that this has been so far accomplished, that the cost for fire-proofing a floor— which also answers for deafening it, is not so much as that of wood used for deaf en-ing or " pugging." The features of this invention willbeeasilyunderstood by the aid of the accompanying engravings. Fig. 1 is a sectional view of the upper and under side of a fire-proof and rat-proof floor with intervening joists and spaces, and also of a vertical wall with sections of lath and concrete. In this engraving the joists are lettered A ; B is the concrete ; C the lath and plaster, or ceiling, on the under side of the floor; D is the floor; E the iron lathing ; F the plastering ; and G the studs. Fig. 2 is a section of the iron laths and the plastering, showing the peculiar form of the laths and the manner inwhich they support the plastering. Fig. 3 is a section of flooring and metallic ceiling for manufactories, etc., in which the letters H represent, respectively, a metallic arch with rib moldings, and also a metallic arch to support the concrete underneath the flooring ; J the joists, and C the flooring. The method of putting on the metallic ceiling is shown in Fig. 4, in which H represents themetallic ceiling, J the joists, K the firring-off clamp, L the nails which secure both the metallic arch and clamp. The whole system will now become perfectly plain to all who have the least knowledge of building, and we think it must be obvious to every candid reader that neither fire can consume, or rats penetrate, a wall of this construction. The basis of these walls is wood, but wood so protected from the external heat, that only a fire of such intensity as to convert the timbers into charcoal, could weaken the main structure. Such an effect could scarcely be produced by the burning of anything but large quantities of the most concentrated fuel inclosed in a building for a long period. The term fire-proof, as applied to buildings, can only be understood to mean proof against the destructive action of fires such as can occur in and around buildings in the course of the ordinary business of life. From what we can judge of this system we think it promises as well, certainly, as any of its rivals; and as the inventor states some ten or twelve first-class buildings are to be erected this season on this plan, its efficacy is evidently believed in by those who are qualified to decide upon its merits. This improved system of constructing fire-proof building has been made the subject of three patents, viz., January 26th April 13th, and May 4th, 1869, by Edwin May, of Indianap olis, Ind., who should be addressed for further particulars. Joint Exposition of tne Wool Industry of tne United States, at the American Institute, In the City of New York. The coming exhibition of the American Institute, which will open on the 8th September and close on the 30th October next, bids fair to be the best exposition yet held by this Association. A feature of great interest is foreshadowed in the fol lowing notice published by the Executive Committee of the National Association of Wool Manufacturers: All American manufacturers of goods composed wholly or in part of wool, and of supplies, machinery, and tools, used directly in the wool manufacture, are invited to exhibit samples of their manufactures at the Joint Exposition of the Wool Industry of the United States, to be held under the auspices of the American Institute, in the city of New York, by the National Associations of Wool Manufacturers and Growers. The place of exposition, on the corner of Sixty-third street and Third avenue, will be open for the reception of goods ou the 1st of September next, and is now open for the reception of machinery. Manufacturers who have agents, or commission houses in the city of New York, are advised to forward their goods through such agents or houses, and to devolve all the charge of their goods upon them. Articles forwarded from other places must be directed to " Wool Industry Exposition, care of N. Kingsbuy, Superintendent, corner of Third avenue and Sixty-third street, New York." The name and residence of the exhibitor, and list of contents, must be marked on the package, the freight and other charges upon which must be prepaid to the place of exhibition. All goods should be forwarded to the Exposition rooms on the 1st of September, or as soon thereafter as possible. Persons desirous to exhibit, who have not already given notice of their intention, are requested to give such notice immediately to N. Kingsbury, Superintendent, care of American Institute, New Yorkcity, or to John L. Hayes, Secretary, Boston, Mass. The notices of intention to exhibit already received, place it beyond a doubt that this will be the most brilliant exposition of the products of a single industry ever seen in this country. Every manufacturer should take pride in contributing to its success, and doing his part to demonstrate the capacity of the United States for industrial independence. Let every mill send a specimen of its products.