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71590 · Moffat & Dobbins · "Improvements in Light Projecting Glasses" · Page 2
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71590: 2 of 5

Page 2
invention shown in the drawing, substantially at a right angle in respect to the prism-bars, these lens-bars presenting outer convex faces, as shown in figure 1.
In the present instance each of the prism-bars has a plane face 3 and a curved or lens-like face 4, for a purpose explained hereinafter; but other forms of prism bar may be used without departing from the main feature of our invention.
The purpose of such lens-bars is to materially increase the effective area of the source from which the glass derives its illumination, lateral rays being caught and transmitted by the convex surfaces of the lens-bars, which would be lost by reflection from a flat surface or from a glass presenting a considerable area of flat surface on the light-receiving side, all of the rays, moreover, being refracted by the lens without that interference with each other which is an objection to light-projecting glasses in which some of the light is transmitted directly, while other rays are refracted and reflected across the path of the direct rays, thus 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