of an iron roof in which the thrust is provided for in a somewhat similiar manner is that designed by the late Mr . J . Scott Russell in the year 1873 , for the Vienna Exhibition building . The roof , as shown in the diagram ( Figure 48 ) , resembles a cone with sides inclined at an angle of 30 °… … the circular base to the apex of the cone and are riveted together . The lower edge is strengthened and supported by a heavy wrought - iron curb or continuous circular box - girder . The upper portion of the cone is removed , leaving an opening 100 feet in diameter , over which is placed another…
