Observe, be very rapid and dextrous in slipping the card at the back of the upright card from its position there to the top of the cards in the palm of your left hand.
SIXTEEN CARDS BEING IN TWO ROWS, TO FIND THAT WHICH A PERSON HAS THOUGHT OF.
The cards being arranged as follow, desire the person to think of one, and to observe well in which row it is:
| A | B | C | D | E | F | H | I |
|---|---|---|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | * |
| 0 | 0 | 0 | 0 | * | 0 | 0 | 0 |
| 0 | 0 | * | 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| * | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Let us suppose that the card thought of is in the row A: take up the whole row in the order in which it now stands, and dispose it in two rows C and D, in such a manner, that the first card of the row A may be the first of the row C; the second of the row A, the first of the row D; and so on, transferring the 16 cards from A and B, to C and D. This being done, again ask in which of the vertical rows the card thought of stands. We shall suppose it to be in C; remove that row as well as D, observing the same method as before; and continue in this manner until the card thought of becomes the first of the row I. If you then ask in which row it is, it may be immediately known, because after the last operation it will be the first in the row said to contain it; and as each row has a distinguishing character or sign, you may cause them all to be mixed with each other, and still be able to discover it by the sign you have remarked.
If a greater number of cards be employed, disposed in two vertical rows, the card thought of will not be at the top of the row after the last transposition: if there are 33 cards, 4 transpositions will be necessary; if 64 there must be 5; and so on.
A CERTAIN NUMBER OF CARDS BEING SHOWN TO A PERSON, TO GUESS THAT WHICH HE HAS THOUGHT OF.
To perform this trick, the number of the cards must be divisible by 3; and to do it with more convenience, the number must be odd.
The first condition, at least, being supposed, the cards must be disposed in three heaps, with their faces turned upwards. Having then asked the person in which heap is the card thought of, place the heaps one above the other, in such a manner that the one containing the card thought of may be in the middle. Arrange the cards again in three heaps, and having asked in which of them is the card thought of, repeat the operation as before. Arrange them a third time in three heaps, and having once more asked the same question, form them all into one heap, that containing the card thought of being in the middle. The card thought of must then necessarily be the middle one; that is to say, if 15 cards have been employed, it will be the eighth from the top; if 21, the eleventh; if 27, the fourteenth; and so on. When the number of the cards is 24, it will be the twelfth, &c.