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Patents: 354 of 530	UNITED STATES PATENT OFFICE. FRANK C. SOPER, OF CHICAGO, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, TO THE LUXFER PRISM PATENTS COMPANY, OF WEST VIRGINIA.	Frank C. Soper 2 of 16
PRISMATIC GLASS. SPECIFICATION forming part of Letter Patent No. 586,247, dated July 13, 1897. Application filed December 28, 1896. Serial No. 617,171. (No model.)

To all whom it may concern:     Be it known that I, FRANK C. SOPER, a citizen of the United States, residing at Chicago, in the county of Cook and State of Illinois, have invented certain Improvements in Prismatic Glass, of which the following is a specification.     My invention relates to prismatic glass, and particularly to such as is designed for use in windows and the like.     I have illustrated my invention and improvement in the accompanying drawings, wherein—     Figure 1 shows an old form of glass, the dotted line showing the direction of a ray of light therethrough. Fig. 2 is another form with my improvement applied. Fig. 3 is my preferred modification.     Like parts are indicated by the same letter in all the figures.     A is the body of the plate of glass; B, a series of prisms thereon, having each a face C and an inclined face D. As shown in Fig. 1, in the old form these faces are all plain.     In Fig. 3, F is a ray of light bent as indicated at G and again as indicated at H. Of course the faces C C may be more or less inclined.     In Fig. 1, J indicates a ray of light which is received on the face C and is reflected away.     K in Fig. 2 indicates a part of the prism which may be removed for certain purposes, thus giving more or less incline to the upper face of the prism.     In Figs. 2 and 3 the action of the curved surface is such that a large number of rays are directed into lines not greatly departing from the horizontal and are thus prevented from being received upon and reflected away by the surface C even when that surface is elevated above the line of parallelism with the course pursued by the light through the glass. The action of the curve is also such as to distribute the light, so as to cause equal quantities of light, so to speak, to fall upon equal surface areas taken perpendicularly to the direction of the light, as indicated by the diagram lines L' L² L³ L4 L5 L6 at different distances from the window along a horizontal line. This curve of course can and must be varied to suit different requirements.

By varying the curve somewhat the light can be directed so that equal quantities of light will fall upon equal horizontal areas at different distances from the window instead of equal vertical areas, as indicated by the diagram of Fig. 3. Moreover, the curves should vary, perhaps, according to the direction from which the greatest quantity of light to be transmitted is received. Under the conditions assumed in Fig. 3 the light is to be received along the lines parallel with the ray F, and it is desired to deliver substantially equal quantities of light over equal vertical areas at different distances from the window, and therefore the curve should be substantially that shown. If the light is to be thrown into more nearly horizontal lines, the surface C may obviously be less inclined than as indicated in Fig. 3 and may even be substantially horizontal, as indicated in Fig. 2, but of course for most practical purposes the light should be distributed somewhat below the horizontal lines, and in such cases with this improvement it is desirable to have the upper surface C very materially inclined with reference to the horizontal.     The prisms in ordinary practice will be uniform, though theoretically they should vary slightly from the bottom of the window to the top. The proper way to ascertain the curvature is to take the average distance of the prisms from the floor and lay off a line to represent this distance. Then place substantially at right angles to this line and at the lower end thereof another line the length of which will approximately represent the length of the area to be illuminated. This area to be illuminated for convenience in the diagram of Fig. 3 is indicated by the horizontal line, which in this case is considered simply with reference to the single prism above it. I now draw a line from the body of glass at the point where the prism curve is to depart therefrom to that point of the line representing the area to be illuminated which is nearest such prism, and at this point I strike a short arc upwardly of any convenient length and join the end of this arc with the point representing the position of the prism. At the intersection of this last line with the area to be illuminated strike another arc of the