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the increase necessary in this case, we draw figure similar to the last, or we use the formula given, and we find that we should multiply the depth by 1.1, i.e. we should make the depth 6½ feet. If we prefer to place this flush, we should have the same amount by increasing it 10 per cent.
    Example 6.--A room 40 feet wide, 50 feet long, 14 feet high, having light walls, and a reveal of 14 inches directly over the window, to be used "For Storage," faces a 25 foot alley, opposite building 80 feet high.
    Solution.--This is the same as problem No. 3, with the exception of the reveal. In problem No. 3 we found a canopy necessary. This introduces no change in the kind of quantity of prisms necessary. The canopy should be set out to clear the reveal.


A Store Lighted From Both Ends.

    In many stores it is desirable to place prisms in each end. These cases may be considered in just the same way as two rooms each lighted from one end, the total length of the two rooms thus considered being equivalent to the long one. We may light the front half of the room from the front end of the store, and the rear half from the rear end, or we may light more than half from the front, say two-thirds, and the remainder from the rear. The proportion of the room which we will light from two ends depends very largely upon the opportunities for light at those ends. The illumination would not be changed to any extent if a white wall there thrown across the room at this imaginary division line. Special attention is called to the fact that simply one end of a store or room cannot be lighted by the area of prisms suggested in the table, unless this end is separated from the remainder by a white wall. If this is attempted the areas of the tables should be increased by 20 per cent.
    Example 7.--A room 25 feet wide, 90 feet long, 17 feet high, to be used "For Fine Merchandise," with no particular obstructions, is to be lighted from both front and rear. The front faces a street 65 feet wide, opposite building 50 feet high. The rear faces a 25-foot alley, with opposite building 80 feet high. Prism plate, 10 feet from sidewalk.
  Pocket Hand-Book of Electro-Glazed Luxfer Prisms - Page 90