invisible writ- and then hidden from view by a flap or loose piece of ing is gently rubbed with slate. (Fig. 1.) After both sides of the slate have been the handkerchief, not too cleaned, the false flap is dropped onto the table, the hard, just enough to let side which is then uppermost being… … ing the audience, becomes suddenly covered with writ- ing, and the slate is immediately given for inspection. The writing is on the slate previous to the cleaning, barely covers the edge of the plate and is fastened to and is hidden from view by a flap of slate colored silk, the paper. held firmly…
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