Magic Trick: The Blackboard Test

The performer seats his assistant, generally a young girl, on the stage, and between her and the footlights he stands a small blackboard. Then he invites one of the audience to come on the stage to act as a committee. Supposing that the girl is on the left of the stage (which is the right of the audience) the performer seats the committeeman on the extreme right. The blackboard is between them, and while the man can see its face from where he sits the girl is too far back to get even a glimpse of it. The performer asks the man to write three lines of five numbers each, one line under another. Before the man begins, the performer blindfolds the girl. To "make assurance doubly sure" he folds two small kid gloves into a wad and places one in each eye of the girl and over these he binds a handkerchief. "All light being now shut out," he says, "please write down your numbers." When this is done, the girl adds up the lines. The secret of the trick is that the performer adds up the columns mentally and then by cues conveys to the girl the particular numbers that she needs to know. These cues are used in sentences addressed to the committee-man in a low voice that does not reach the audience. The performer never speaks to the girl, unless she makes a mistake. In that case he gives her the proper cues. These cues consist of the first consonant of the first word in the sentence. To make this clear let us suppose that

 1 is represented by T or D, as in This, That, There, Do, Does, Don't 2 is represented by N, as in Now, Name 3 is represented by I, as in I, In 4 is represented by R, as in Right, Write 5 is represented by L, as in Let, Look, Well, Will 6 is represented by J, as in Just 7 is represented by C hard, as in Can, Come, Quick, Go 8 is represented by H, as in Have, Here, How 9 is represented by P or B, as in Please, Be good 0 is represented by S, as in See, Sir

Let us illustrate this by supposing that the committeeman writes the following numbers:

 9 7 5 3 1 2 4 6 8 0 1 3 5 7 9

These add up 135,790. The performer foots up the first column mentally, and turning to the committeeman, who is to add up the column and write the sum, he says, for instance: "T1hat will do. S0ee that your figures are plain." The girl mumbles to herself, as if adding up the figures and calls out, "Put down naught and carry one." For the second column the performer may say: "T1here, that's good. P9lease move so that the audience can see." Again the girl begins to mumble, and says: "Nineteen. Put down nine and carry one." For the third column, which adds up 17, he may say: "T1hat's fine. Q7uick work, isn't it?" For the fourth column, "D1own, all right. Well5, go on;" for the fifth column: "T1hat's all. I3 am obliged, Sir." The audience do not hear and the committeeman imagines that he is merely speaking in praise of the girl's work, and cleverness.

When the sum of the columns is written down, the performer hands the committeeman a light cane and requests him to point out or rather to touch some number. He does so and at the same moment the girl calls out the number. In this way three or four numbers are told. For this phase of the trick the performer uses other cues which he addresses to the committeeman. He is watched closely and just as his stick is about to touch a number the performer says (1) "Any one"—(2) "Any number;"—(3) "Any number you choose;"—(4) "Take any;"—(5) "Take any number;"—(6) "Take any number you wish;"—(7) "Choose any;"—(8) "Choose any number;"—(9) "Choose any number you wish"—(0) "All right."

When the committeeman is through the performer picks up the stick and rapidly points from one number to another, the girl, as rapidly, calling out the name. This is, simply a line of prearranged numbers, as, for example, the years in which the girl and the performer were born, but called out backward. Those familiar with the mnemonic cues will find it easy if they will take a line from some familiar song, as, for instance, "D1on2't1 you r4em3em3b9er4 S0weet1 Al5ic0e, B9en2 B9ol5t1," or "Hail5 C7o5lum3b9ia Hap9py L5an2d1." Now and then, by previous arrangement, the performer points above or below a number, and the answer, "There's nothing there," is generally greeted with a laugh.

In describing the blindfolding of the girl we mentioned that the performer first placed a kid glove over each eye. This, instead of blinding her further, really helps her to see, for when the performer is putting the handkerchief around her eyes, she assists him by holding it, and at the same time moves the gloves so that they are on her eyebrows. This keeps the handkerchief away from her eyes, and she is enabled by looking down to see what is going on.

Another way of conveying the numbers is by the position on the back of the board of the fingers of the hand that holds the blackboard, as shown in the illustrations. Number 1 is represented by turning in the first finger; number 2 by turning in the first and second fingers; number 3 by the first, second, and third fingers turned in, and number 4 by turning in all four fingers. For number 5 three fingers lie flat and the second finger of the hand is turned in, the 3 and 2 equaling 5; numbers 6 and 7 are shown in the same way, that is, three fingers are flat and the third finger of the hand is turned in, in the one case, and three are flat and the fourth finger of the hand is turned in the second. Number 8 has all four fingers lying flat, and number 9, all four fingers flat, but spread apart. For 0 the index finger and the little finger lie flat and the second and third fingers are turned in. For 10 the four fingers lie flat, but the index is spread away from the others; for 20 the four fingers also lie flat, but the forefinger and the second are kept together but spread apart from the others; for 30 the four fingers are again laid flat with the little finger spread apart from the others.

There is still another way of communicating numbers, and that is by dividing the face and the body into squares by imaginary perpendicular and horizontal lines. Each of these imaginary squares is numbered, say, as shown in Fig. 191: The right side of the forehead, = No. 1; the right ear, = No. 4; the right jaw,= No. 7; the middle of the forehead, = No. 2; the nose,= No. 5; the chin,= No. 8; the left side of the forehead, = No. 3; the left ear,= No. 6; the left jaw,= No. 9; any part of the neck or throat, = 0. In the same way, the body is divided: The upper right side on a line with the shoulder, = 1; the right side, lower down,= 4; near the right lower pocket of the vest, = 7; the upper part of the body, just below the chin,= 2; about the pit of the stomach, = 5; about the center of the waist,= 8; the upper left side, on a line with the shoulder, = 3; about the center of the left side,= 6; the region of the left lower pocket of the vest, = 9; and at the bottom of the vest in the center, = 0. In addition to this, the stage curtain or the space it occupies is also divided into imaginary lines, numbered in the same way, and by looking up or down or straight ahead; by turning the head to either side, and directing his glance toward the spot occupied by these imaginary numbers, the performer can give his assistant any number in the imaginary squares. At other times numbers, especially the decades ten, twenty, and thirty are signaled by taking a step forward, backward or to one side, as agreed upon between the performer and his assistant. By combining these various methods any number under a thousand may be conveyed rapidly and imperceptibly. Of course a great deal of tact is needed in order to give the cues in a natural way, so as not to excite suspicion. That it is done successfully is unquestionable, but not to any great extent for two reasons; first, it is not generally understood, and secondly, it requires considerable rehearsing.

Fig. 191

Much thought has been spent on the different silent methods of communicating numbers. One of these is synchronous counting, that is, two people count together in the same time, studying this by means of a metronome. This requires a very correct ear, and at best is liable to errors. Another and better method is that in which the performer counts the breathing of his assistant by watching the rise and fall of her breast. The most simple and in our opinion the best is by means of our reliable old friend, a length of fine black silk thread. One end of this is tied to the assistant's thumb, the rest of it she holds in her hand. When the performer bandages her eyes, she passes the thread to him. He takes his position alongside the blackboard, and by a prearranged system of long and short jerks conveys to her the required numbers.

A well known performer gives a very striking example of what he calls his control of his wife's mind by allowing some person to select any page in a book and to choose a line in that book. He holds the book and his wife soon after opens a second copy of it at the page selected and begins to read at the very line chosen. Our readers will at once see how easy it is to convey to her the number of the page and the line by means of his fingers at the back of the book, combined with one or more of the methods we have described.