We have never been able to understand the reason why iron has so long been neglected as a covering for roofs, but are gratified to learn that Mr. Wm. Beach, of Troy, N. Y., has invented and patented a mode of using cast iron plates for covering roofs. They are about one foot square, and are made to fit one into another, so as to render the roof water tight, by applying white lead to the joints. It can be afforded at 16 cents the square foot, and probably may be so far improved as to cost no more than slate, and will be much more permanent and safe. We see no difficulty in dispensing with white lead, however, and making the seams tight without it. =Improvement in the Railroad Track.= This improvement was entered Sept. 5th, by John F. Rogers. What he claims is the combination of the balance beam with the centre beam, by means of the recesses in the centre beam, spring plates, having tubes thereon on which the springs rest, and attached to the beam by bolts, by which a compact and secure connection is formed, while all the necessary flexibility is preserved. =THE GREAT FAIR.= The American Institute appears emblematical of the genius of our countrymen--unsubdued even by conflagration, and looking upon obstacles as incentives to redoubled effort. Contrast the smoking ruins of Niblo's with Castle Garden, having its whole amphitheatre enriched with a tastefully arranged collection of the most varied products of American arts and manufactures, and behold an evidence that we even inherit perseverance, enterprize and skill. We here see the embodiment of the excellence of greatness of our country--an unerring index of our future advance--if it be not that the signs of the times indicate that madness in our rulers which precedes and forebodes heaven's wrath. But it cannot, it must not be, that the blood of _labor_ shall cry from the ground of America. It must be sheathed, it must be protected. Protection is nature's first law. Expose the bleating flocks to the hungry beasts of the forest; cut the wings and pluck the feathers of her whom nature teaches to protect her brood from cold and rain; say to the mother to leave her babe unprotected and in free competition with all the elements of destruction, sooner than refuse the protection of our Government to the hitherto flourishing American manufactures. Castle Garden, or more correctly Castle Clinton, is at the southern extremity of our city. It was built for a fort--is of a circular form, of solid mason work, surrounded by the waters of the bay--connected to that ornament of the city, the Battery, by a long bridge. This bridge the managers have covered with a roof, and thus secured a very eligible and spacious apartment for the exhibition of carriages, sleighs, carts, farming implements and machinery in great variety. Thence the ingress suddenly opens into view the whole interior, creating the most lively and pleasing emotions.