The most familiar examples of mnemonic books are the quipus or knotted cord books, the notch books, which include tallies and message sticks, the wampum belts of American Indians, and the abacus. Collections of any of these kept in the medicine tent or temple, or even the counting house, are, of course, true libraries, or at least true collections of written documents as generally understood by the historians of writing. The knotted cord is best known under the name of quipu, which was the name for the Peruvian knot record. At bottom the idea does not differ from the simple tying of knots in a handkerchief as a reminder, or the sailor’s log line. It has been most commonly used for numerical records, but in many cases it preserved and transmitted very extensive historical records. One very simple use was the noting on different colored cords by knots the number of the different animals taken to market for sale, and again the price received for these at market. It is still used among the Indians of Peru and some North American Indians, also in Hawaii and among various African tribes, and all over Eastern Asia and the Pacific. It was the traditional method in China before the use of written characters, and the written characters themselves were, it is alleged, made up out of these combined with the pictures of bird tracks. Among the ancient civilizations there are many remains or reminiscences of these knot books. They are found among the ancient Egyptian hieroglyphics (as in the sign for amulet and perhaps in several other signs); they appear also in the mnemonic knotted fringes to garments in the Jewish antiquities and, as Herodotus tells us, Darius made use of such knots to guide certain Ionians who remained behind to guard a bridge as to when it should be time for them to sail away. In 1680 the Pueblo Indians of North America marked the days to their uprising in the same way. This use of the knotted cord for amulets is among the most widespread of uses, being found among the medicine men of nearly all primitive peoples. Juno wore such an amulet, and Ulysses carried one. Among the ancient Peruvians and Mexicans there were many collections of quipus in charge of official recorders. Traces of ancient use survive in the knots of a cardinal’s hat and perhaps most interestingly of all in the nautical knot used in casting the log or sounding. We may still travel so many knots an hour or sink mayhap so many fathoms deep. The knotted measuring line with fathom marks is probably the direct historical descendant of the Egyptian measuring line and by the same token probably of the Egyptian sign for one hundred, the fathom like one of the Egyptian units being at bottom the stretch of a man’s arm. [Illustration: A COLLECTION OF MESSAGE STICKS FROM HOWITT. NATIVE TRIBES OF S. E. AUSTRALIA, p. 704 ]