In addition to a wooden back, the mirror had a cloth back, which was firmly fastened into the frame. The wooden back was hinged to the frame at the bottom, and was very strong.
When the frame was placed on the easel and the mirror rested on the floor, the space behind the easel from the floor up was entirely hidden. This was done when Merry took the mirror apart to exhibit it.
At that moment M. Mazarin came up through a trap-door in the floor and let down the wooden back of the frame, which formed a shelf, and on that shelf he could rest with ease. When the mirror was returned to the frame, the audience could look through beneath it, and no one could suspect that a human being was concealed back of it.
The black cloth was divided off into squares to correspond with those afterward marked on the mirror with the soap. The squares were numbered and lettered precisely the same, so that the assistant knew where every character was located on the face of the mirror.
The assistant behind the mirror was provided with a strong electro-magnet, attached to a wire running down one leg of the easel to a powerful battery under the stage.
When the assistant heard the numbers called, he placed his magnet opposite the corner where the fly was resting, and then moved it along the back of the mirror to the required square. In that manner he was able to add, subtract, multiply and divide.
The buzzing of the fly was produced by Merriwell himself, who imitated the proper sound.
Frank located Sport Harris, and recognized the fellow. Then, standing near the mirror, he whispered to Mazarin the name he wished him to spell with the aid of the magnetized fly.
Thus it will be seen that this apparently marvelous performance was in truth a "fake," and not at all difficult to give. But it was always successful when properly done.
Merry took care of the apparatus, and then looked over the other stuff, locking up such things as he did not wish to leave out to be inspected by curious eyes.
When this was done, he went to the box office, where he found Burnham waiting for him.
"What's the matter with Mazarin?" asked the manager of the opera house.
"He has been here growling like a dog with a sore ear."
"He thinks Zolverein did not use him right in giving the apparatus to me."