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280   Art of Travel.

in fig. 2, and are reduced by its agency to parallelism with r' and R', that is, with the rays that originally left the mirror consequently E, looking partly at the edge of the lens, and

partly into space, sees a bright speck of light in the former, coincident with the point o in the latter. What is true for one point in the sun's disc, is true for every point in it. Accordingly, the signaller sees an image of the sun, and not a mere speck of light, in the lens ; and the part of the landscape

-which that image appears to overlay, is precisely that part of