TEST IN ADDITION.
In this experiment the performer brings forward an ordinary slate and piece of crayon and requests some person to write a column of figures on the slate. The performer now takes the slate, quickly draws a line underneath the column of figures, and places the slate, face downward, on a table, on the top of slate placing a small piece of crayon. His assistant, who has been out of the room during this part of the experiment, now enters, and on walking up to the slate picks up the crayon and marks down the total sum of figures on the other side of the slate, which are found to be absolutely correct on turning the slate over and adding the figures up.
To perform this experiment the performer is armed with a small piece of crayon in addition to the crayon which he gives to the spectator. One side of the crayon which he retains is filed smooth. The performer also has a small lead pencil concealed in his hand along with the crayon. When the person in the audience is writing down the figures the performer mentally adds these up, and secretly writes the sum total on this small piece of chalk which he has in his hand. He now takes the slate, places it face downward upon the table, and on top of it places the prepared piece of chalk, flat side down, retaining the chalk which the spectator used. All that is now necessary is for his assistant to pick up the piece of chalk, secretly read the figures written on it, and mark them down upon the slate.