Prismatic beam concentrator
BACKGROUND OF THE INVENTION 
     The invention relates to optics, specifically to prisms. 
     The use of prisms for the refracting of beams in one dimension is well established in the art. A beam transmitted into a prism through a perpendicular face and refracted out of the prism through an angular face is reduced in width. Prismatic beams are afocal, and this means that a beam can be refracted and reduced in width several times. This is illustrated in Sanagi&#39;s Luminous Flux Apparatus Using Prisms, Japan Pat. No. 119,260. 
     SUMMARY OF THE INVENTION 
     The use of indirect sunlight as a source of energy imposes the problem of how to derive enough heat from such a low-heat source to make the system economically feasible. The heat content of diffused sunlight is very low, and this means that a very large incipient beam must be reduced in width to a very small concentrated beam. 
     One solution of the problem is to use two or more prisms stacked vertically in stages to reduce the width of the beam several times. This is known as multiple concentration, and it has been used successfully in several patented beam concentrators. 
     The disclosure offers an alternative to multiple concentration. Instead of stacking a number of prisms vertically to produce successive concentrations of a beam, a number of prisms with tapered rectangular blocks can be arranged in a semicircle around a heat duct so that the concentrated rays converge on the surface of the duct. Moreover, the alternative offers a slight advantage when a duct with a large diameter is used, because a number of concentrated beams converging from different angles are displayed more evenly on the surface of the duct than a single beam. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevation of the prismatic beam concentrator with the prisms shown in section. 
     FIG. 2 is an elevation of the concentrator with a ray diagram. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is an elevation of the prismatic beam concentrator comprising a bilateral prism 1, an intermediate adjoining section 2 and a tapered rectangular block 3. The prism is bisected by the vertical prismatic plane (not shown). 
     Tapered rectangular block 3 is a solid bound by six planar sides; two opposed parallel upper and lower sides 4 and 5, two opposed parallel front and rear sides 6 and 7, and two opposed lateral sides 8 and 9 inclined at equal angles to the vertical prismatic plane. A rectangular slot 10 is located in the center of the block to serve as an aperture through which the concentrated beam passes. 
     FIG. 2 shows two concentrators mounted side by side above a horizontal heating duct 11. Lateral side 8 of the concentrator on the right is in contact with lateral side 9 of the concentrator on the left. Two convergent rectangular incipient beams 12 of diffused sunlight are received and transmitted into the prism by two angular wedge faces 13 and 14 and refracted and emitted by two angular V-groove faces 15 and 16, forming concentrated sheet beam 17 which is emitted through slot 10 onto conduit 11. 
     The purpose of tapered rectangular block 3 is to provide semicircular alignment of two or more prisms around the heat duct so that the concentrated beams will converge on the surface of the duct as shown in FIG. 2. The outermost incipient beams should not fall below the horizon, and this means that a maximum of three prisms can be used effectively when the heat duct is mounted horizontally.