EXPLANATION.--Touch the cards at random during the first seven taps and allow your pencil, on its eighth tap, to rest on the king (twelve). Eight and twelve being twenty he will of course say "Stop." Supposing he thought of a lower figure--seven, for instance. Tap at random as before until your eighth tap, which must always be on twelve; then touch the cards in rotation, making the queen your ninth tap, the ten your tenth tap, nine your eleventh, and so on until you reach seven, which will be your thirteenth tap, which number added to seven, the number thought of, will make twenty, and your friend will say "Stop."
Another effective trick can be worked with the card dial, but it requires the assistance of a confederate. Having previously instructed him what to do, you tell the company that any one is at liberty to touch one of the cards during your absence from the room, and on returning you will indicate the card he has touched. Upon your returning hand a pencil to your confederate and request him to touch the cards in rotation until you say "Stop," when the pencil will rest on the right card. Your confederate must hold the pencil in his right hand with his forefinger resting on top. When he touches the right card he must raise that finger slightly. It is a signal no one would notice, and the trick always creates a great deal of wonder.
Allow the pack to be shuffled freely and then place it on the table face down. Take the three top cards, and holding them up with their backs towards you, ask some one to think of one. Then spread them face down on the table in front of you. Take three more cards, and ask a second person to think of one, and lay these on top of the other three. Show three more cards to a third person, and after he has thought of one, lay these on top of the others. You have now three parcels on the table, each containing three cards. Hold up one parcel, and say to each person: "Is the card you thought of in this lot?" Proceed in the same way with the other parcels, and then tell each person the name of the card he thought of. As the cards shown to the first person were laid on the table first, it stands to reason that the cards he thought of must be at the bottom of the parcel he has said "Yes" to; the second person's card will be the middle one in the parcel, and the third person's the top card.