Kay, speaking of visualization, or the reproduction of mental images of things to be remembered, says: “Those who have been distinguished for their power to carry out long and intricate processes of mental calculation owe it to the same cause.” Taine says: “Children accustomed to calculate in their heads write mentally with chalk on an imaginary board the figures in question, then all their partial operations, then the final sum, so that they see internally the different lines of white figures with which they are concerned. Young Colburn, who had never been at school and did not know how to read or write, said that, when making his calculations ‘he saw them clearly before him.’ Another said that he ‘saw the numbers he was working with as if they had been written on a slate.'” Bidder said: “If I perform a sum mentally, it always proceeds in a visible form in my mind; indeed, I can conceive of no other way possible of doing mental arithmetic.”

We have known office boys who could never remember the number of an address until it were distinctly repeated to them several times–then they memorized the _sound_ and never forget it. Others forget the sounds, or failed to register them in the mind, but after once seeing the number on the door of an office or store, could repeat it at a moments notice, saying that they mentally “could see the figures on the door.” You will find by a little questioning that the majority of people remember figures or numbers in this way, and that very few can remember them as abstract things. For that matter it is difficult for the majority of persons to even think of a number, abstractly. Try it yourself, and ascertain whether you do not remember the number as either a _sound of words_, or else as the mental image or visualization of the _form of the figures_. And, by the way, which ever it happens to be, sight or sound, that particular kind of remembrance is _your_ best way of remembering numbers, and consequently gives you the lines upon which you should proceed to develop this phase of memory.

The law of Association may be used advantageously in memorizing numbers; for instance we know of a person who remembered the number 186,000 (the number of miles per second traveled by light-waves in the ether) by associating it with the number of his father’s former place of business, “186.” Another remembered his telephone number “1876” by recalling the date of the Declaration of Independence. Another, the number of States in the Union, by associating it with the last two figures of the number of his place of business. But by far the better way to memorize dates, special numbers connected with events, etc., is to visualize the picture of the event with the picture of the date or number, thus combining the two things into a mental picture, the association of which will be preserved when the picture is recalled. Verse of doggerel, such as “In fourteen hundred and ninety-two, Columbus sailed the ocean blue;” or “In eighteen hundred and sixty-one, our country’s Civil war begun,” etc., have their places and uses. But it is far better to cultivate the “sight or sound” of a number, than to depend upon cumbersome associative methods based on artificial links and pegs.

Finally, as we have said in the preceding chapters, before one can develop a good memory of a subject, he must first cultivate an interest in that subject. Therefore, if you will keep your interest in figures alive by working out a few problems in mathematics, once in a while, you will find that figures will begin to have a new interest for you. A little elementary arithmetic, used with interest, will do more to start you on the road to “How to Remember Numbers” than a dozen text books on the subject. In memory, the three rules are: “Interest, Attention and Exercise”–and the last is the most important, for without it the others fail. You will be surprised to see how many interesting things there are in figures, as you proceed. The task of going over the elementary arithmetic will not be nearly so “dry” as when you were a child. You will uncover all sorts of “queer” things in relation to numbers. Just as a “sample” let us call your attention to a few:

Take the figure “1” and place behind it a number of “naughts,” thus: 1,000,000,000,000,–as many “naughts” or ciphers as you wish. Then divide the number by the figure “7.” You will find that the result is always this “142,857” then another “142,857,” and so on to infinity, if you wish to carry the calculation that far. These six figures will be repeated over and over again. Then multiply this “142,857” by the figure “7,” and your product will be _all nines_. Then take any number, and set it down, placing beneath it a reversal of itself and subtract the latter from the former, thus:

117,761,909 90,916,771 ———– 26,845,138

and you will find that the result will always reduce to nine, and is always a multiple of 9. Take any number composed of two or more figures, and subtract from it the added sum of its separate figures, and the result is always a multiple of 9, thus:

184 1 + 8 + 4 = 13 —- 171 รท 9 = 19

We mention these familiar examples merely to remind you that there is much more of interest in mere figures than many would suppose. If you can arouse your interest in them, then you will be well started on the road to the memorizing of numbers. Let figures and numbers “mean something” to you, and the rest will be merely a matter of detail.