Modern Magic: A Practical Treatise on the Art of Conjuring

Now it would seem at first sight sufficiently surprising that I should be able merely to tell you the number of dominoes which have been moved in my absence, but that might be easily effected by confederacy, or many other very simple expedients. I propose to do much more than this, and to show you not only that I know the number that you have just displaced, but that I can read the dominoes before you as readily in their present position as though they were lying face upwards. For instance, this domino” (touching one of the row with your finger or wand) “represents the number which have been moved in my absence. Will some one please to say what that number was?” The answer is, we will suppose, “Seven.” “Seven,” you repeat, turning over the domino you have touched. “You see that I was right. Would you like me to name some more? They are all equally easy. This, let me see--yes, this is a two; this is a nine; this is a double-six; this is a double-blank;” turning over each domino to show that you have named it right.