The cards moved are not replaced, but the performer again retires, and a second person is invited to move a few more from right to left. Again the performer on his return takes up the correct card indicating the number shifted. The trick, unlike most others, may be repeated without fear of detection.
The principle is arithmetical. To begin with, the cards are arranged, unknown to the spectators, in the following order:
Ten, nine, eight, seven, six, five, four, three, two, one.
Such being the case, it will be found that, however many are shifted from right to left, the first card of the new row will indicate their number. Thus, suppose three are shifted. The new order of the cards will then be:
Three, two, one, ten, nine, eight, seven, six, five, four.
So far, the trick is easy enough, but the method of its continuance is a trifle more complicated. To tell the position of the indicating card after the second removal, the performer privately adds the number of that last turned up (in this case three) to its place in the row—one. That gives us four, the card to be turned up after the next shift will be the fourth. Thus, suppose six cards are now shifted, their new order will be:
Nine, eight, seven, six, five, four, three, two, one, ten.
Had five cards only been shifted, the five would have been fourth in the row, and so on.
The performer now adds six, the number of the card, to its place in the row, four: the total, ten, gives him the position of the indicator for the next attempt. Thus, suppose four cards are next shifted, the new order will be:
Three, two, one, ten, nine, eight, seven, six, five, four.