causing interference which materially detracts from the light projecting properties of the glass.

The lens bars also serve to cause lateral diffusion of the light projected by the glass, and thereby correspondingly increase the area which can be effectively illuminated.

We wish to avoid all internal reflection from the lens surface of the glass when said lens surface -is presented to the incident ray, and for this reason the lens bars are shallow or of such a considerable radius of curvature that an incident ray striking any part of the curved surface of the lens bar and refracted thereby cannot reach any internal surface of the lens bar so as to be reflected, but will, after refraction, pass directly through the glass until it reaches the opposite prism surface.

One of the advantages of a light projecting glass constructed in accordance with our invention is that it may occupy a relation in respect to the upper portion of a window opening which is the reverse of the usual awning or canopy position thereby permitting the direct transmission of light through the upper portion of the window opening in addition to that which is projected therethrough by the glass, thus insuring the lighting of an area close to the window and over- coming a defect in prism glasses as ordinarily used, which rob the areas near the window openings of light for the benefit of the portions to which the latter is projected.

We may state that one -of the incidental advantages of our invention is that the lens bars very materially increase the strength of the glass and permit us.to produce glasses of larger area than is possible in making light projecting glasses of ordinary character.

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:—