Years ago when I introduced this trick in my performance, I called a young man on my stage and asked him to place the hand on the spindle. It would then revolve and stop at any number named. But first I made him inform the audience the number he had chosen, which gave me time to fix the weight with my thumb. I then gave him the hand, but he was a skilled mechanic, and possibly knew the trick. Instead of holding the clock by the ring at the top, which was there for that purpose, he grasped the dial at the bottom, causing the number 6 instead of 12 to be on top. When the hand started to turn, of course it would have stopped at the wrong number. I managed to escape humiliation by pretending I was afraid he would break the clock by letting it fall, so took it away from him, holding it myself.
The mechanic walked off the stage winking at me in the most roguish manner.
Robert-Houdin worked The Mystic Bell trick in connection with The Clock. This was manipulated in the same way. The bell was worked with thread, pulling a small pin, which in turn caused the handle to fall against the glass bell. Naturally, having electricity at his command at that time, he made use of that force whenever it suited his fancy.
I am positive that Robert-Houdin presented the electrical clock, because T. Bolin, of Moscow, visited Paris and bought the trick from Voisin, the French manufacturer of conjuring apparatus. The trick which Robert-Houdin presented, according to his claims, was with the clock hanging in midair to prove that it was not electrically connected, but the truth of the matter is that the strings which held the clock suspended in midair concealed the wires through which his electrical current ran.