We, DEUTSCHE GLASBAU-GESELLSCHAFT M.B.H, a corporation organized under the laws of Germany, of 43, Lehliderstrasse, Berlin-Weissensee, Germany, do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement:—

The invention relates to the construction of floor slabs, wall panels, pavement lights, windows and the like in which discs or cylindrical bodies of glass are framed in ferro concrete, the invention being concerned with moulds for moulding the concrete by the usual method of placing the moulds on a moulding board or in a frame or box, with the glass bodies upon them, and pouring the concrete into the channels between the walls of the moulds, so that after removing the moulds there is a concrete frame consisting of ribs extending crosswise, enclosing openings in each of which a glass body is held.

For making the concrete frame the moulds preferably have a rectangular base, so that they can be set closely together on the moulding board, but they have circular openings corresponding in diameter to the glass bodies. Consequently the configuration of the moulds must be one in which there is a transition from square to circular outline.

The greater the depth of the ribs, the less light can pass through such a structure, inasmuch as the ribs intercept and reflect light, not all of which passes out of the frame, but for adequate strength the ribs must frequently be of substantial depth, as when there is heavy traffic on a floor of which they form part.

The usual form of mould is one in which the rectangular base merges, towards the circular opening, into a rounded part in the form of a hollow, truncated cone.

According to our invention the illuminating capacity of the structure is increased by using a mould with a square base from which four sides rise to form a

hollow, truncated pyramid, but are outwardly concave and have their top edges bent to form the circular opening, the meeting edges of the sides being lengthened to make corners which make an obtuse angle with the plane of the opening. The construction of the moulds enables a greatly increased amount of light to pass through the structure, inasmuch as pockets are formed at the corners of the openings in which the glass bodies are held, and a large proportion of the inclined light rays which would otherwise be intercepted are able to pass freely through these pockets. This is of particular advantage in the case of built-in, arched roofs, where the available light is generally weak near the walls. The weight of the floor is also reduced by the absence of concrete in the pockets, so that the depth of the ribs can be reduced.

A portion of a floor or pavement light constructed with the use of moulds according to the invention is shown by way of example in the annexed drawings,

Fig. 1 being a perspective view thereof, with a portion broken away at one corner.

Fig. 2 shows several moulds on a moulding board, one of them partly broken away.

Fig. 3 is a bottom plan view of one of the moulds,

Figs. 4 and 5 being, respectively, sections on the lines A—B and C—D of Fig 3.

Figs. 6 and 7 represent portions of the finished structure, in section on lines corresponding to the lines A—B and C—D respectively of Fig 3.

Each of the mould members has a square base a from which the four sides e rise to form, roughly, a hollow, truncated pyramid, but with inward curves e¹ near the base (Fig. 4), so that at its lower part the mould is outwardly slightly concave, and inwardly convex. The corners f are, accordingly, acute angled.

For producing circular openings in accordance with the shape of the