Fig. 116.
To Change, invisibly, the Numbers shown on either Face of a Pair of Dice.—Take a pair of ordinary dice, and so place them between the first finger and thumb of the right hand (see [Fig. 116]), that the uppermost shall show the “one,” and the lowermost the “three” point, while the “one” point of the latter and the “three” point of the former are at right angles to those first named, and concealed by the ball of the thumb. (The enlargement at a in the figure shows clearly the proper position.) Ask someone to name aloud the points which are in sight, and to state particularly, for the information of the company, which point is uppermost. This having been satisfactorily ascertained, you announce that you are able, by simply passing a finger over the faces of the dice, to make the points change places. So saying, gently rub the exposed faces of the dice with the forefinger of the left hand, and, on again removing the finger, the points are found to have changed places, the “three” being now uppermost, and the “one” undermost. This effect is produced by a slight movement of the thumb and finger of the right hand in the act of bringing the hands together, the thumb being moved slightly forward, and the finger slightly back. This causes the two dice to make a quarter-turn vertically on their own axis, bringing into view the side which has hitherto been concealed by the ball of the thumb, while the side previously in sight is in turn hidden by the middle finger. A reverse movement, of course, replaces the dice in their original position. The action of bringing the hands together, for the supposed purpose of rubbing the dice with the opposite forefinger, completely covers the smaller movement of the thumb and finger.
Fig. 117.
After having exhibited the trick in this form once or twice, you may vary your mode of operation. For this purpose take the dice (still retaining their relative position) horizontally between the thumb and second finger, in the manner depicted in [Fig. 117], showing “three-one” on their upper face; the corresponding “three-one,” or rather “one-three,” being now covered by the forefinger. As the points on the opposite faces of a die invariably together amount to seven, it is obvious that the points on the under side will now be “four-six,” while the points next to the ball of the thumb will be “six-four.” You show, alternately raising and lowering the hand, that the points above are “three-one,” and those below “six-four.” Again going through the motion of rubbing the dice with the opposite forefinger, you slightly raise the thumb and depress the middle finger, which will bring the “six-four” uppermost, and the “three-one” or “one-three” undermost. This maybe repeated any number of times; or you may, by moving the thumb and finger accordingly, produce either “three-one” or “six-four” apparently both above and below the dice.
The trick may, of course, be varied as regards the particular points, but the dice must, in any case, be so placed as to have similar points on two adjoining faces.
To Name, without seeing them, the Points of a Pair of Dice.—This is a mere arithmetical recreation, but it is so good that we cannot forbear to notice it. You ask the person who threw the dice to choose which of them he likes, multiply its points by two, add five to the product, multiply the sum so obtained by five, and add the points of the remaining die. On his telling you the result, you mentally subtract twenty-five from it, when the remainder will be a number of two figures, each representing the points of one of the dice.
Thus, suppose the throws to be five, two. Five multiplied by two are ten; add five, fifteen, which, multiplied by five, is seventy-five, to which two (the points of the remaining die) being added, the total is seventy-seven. If from this you mentally deduct twenty-five, the remainder is fifty-two, giving the points of the two dice—five and two. But, you will say, suppose the person who threw had reversed the arithmetical process, and had taken the points of the second die (two) as his multiplicand, the result must have been different. Let us try the experiment. Twice two are four, five added make nine, which, multiplied by five, is forty-five, and five (the points of the other die) being added to it, bring the total up to fifty. From this subtract twenty-five as before. The remainder, twenty-five, again gives the points of the two dice, but in the reverse order; and the same result will follow, whatever the throws may be.
