cylindrical glass bodies d the moulds must have circular apertures at the top, and this is produced by bending the top edges c of the sides e so that they form complementary arcs of the requisite circle. Also, the corners f are lengthened, so that the sides e continue to meet, at the corner, at an acute angle and with concave formation right up to the rim of the circular aperture. At the corners the angle β made by the meeting edges f with the plane of the aperture (Fig. 5) is considerably more obtuse than the angle α made with that plane by the central portions of the sides e.

The floor or pavement light is constructed in the usual way by placing the moulds in rows in a moulding frame or box h, with the glass bodies d upon them, and then placing the iron reinforcing bars o in the channels between the side walls and pouring in the concrete. When the concrete has set and the moulding frames have been removed the glass bodies are firmly held by a framework of intersecting ferro-concrete ribs i, k enclosing rectangular fields m, and by reason of the shape given to the moulds there are at the corners of each field m hollows or pockets f¹, the walls of which make, with the surface of the glass floor, the angle β, which is substantially more obtuse than the angle made by those parts of the ribs i, k which lie centrally between the corners or the field.

Light rays striking the floor perpendicularly pass freely through to the room

below, but inclined rays, such as the rays X—X indicated in Figs. 6 and 7 in part strike the ribs (Fig. 6), in which case some of them are absorbed and some are reflected into the room. The greater the depth of the ribs, the more rays are thus reflected. At the corners however, inclined rays X—X can pass through directly. The pockets referred to do not weaken the structure, but substantially increase the amount of light which the room receives.

The moulds may be made of any convenient material, and may if desired or necessary remain permanently in the structure.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is:—

A mould for the purpose set forth having a square base from which four sides rise to form approximately a truncated, hollow pyramid having outwardly concave sides, with the top edges bent to form a circle and the meeting edges of the sides extended to the rim of the circle to form corners which make an obtuse angle with the plane of the circle.