MNEMON [CS, or artificial helps to the memory, have been employed in a more or less systematic form from a very early period. Mnemonics (-a that the strength of his memory- was famous. Cicero, who of Carneades (or perhaps Charmades) of Athens and Metrodorus of Scepsis as distinguished examples of the use of well-ordered images to aid the memory. The latter is said by Pliny to have carried the art so far ftt nail non iisdem verbis redderet auditum. The Romans valued such helps as giving facility in public speaking. The method used is described by the author of Rhet. ad Berm, 624; see also Quintilian (inst. Or., x.1, 2), whose account is, however, somewhat incomplete and obscure. In his time the art had almost ceased to be practised. The Greek and Roman system of mnemonics was founded on the use of mental places and signs or pictures. The thing to be remembered was localized in the imagination, and associated with a symbol which concretely represented what it was desired to retain in the memory, special care being taken that the symbols should be as vivid, pleasing, and impressive as possible. The most usual method was to choose a large house, of which the apartments, walls, windows, statues, furniture, kk.7c., were severally associated with certain names, phrases, events, or ideas, by means of symbolic pictures ; and to recall these it was only necessary to search over the apartments of the house, till the particular plan: was discovered where they had been deposited by the imagination. As the things to be remembered increased, new houses could be built, each set apart to a certain class of ideas or events, and these houses were again constructed into a mnemonic town. In accordance with this system, if it were desired to fix an historic date in the memory, it was localized in an imaginary town divided into a certain number of districts, each with ten houses, each house with ten rooms, and each room with a hundred quadrates or memory-places, partly on the floor, partly on the four walls, partly on the roof. Thus, if it were desired to fix in the memory the date of the invention of printing (1436), an imaginary book-, or some other symbol of printing, would be placed in the thirty-sixth quadrate or memory-place of the fourth room of the first house of the historic district of the town. The success of the method depended largely on the power of the imagination to give the different houses, rooms, &c., characteristic varieties of aspect, and we may-suppose that it was the effort to frame suitable images and places, giving an adventitious interest to dry details, that constituted the real advantage of the system. Except that the rules of mnemonics are referred to by Martianus Capella, nothing further is known regarding the practice of the art until the 13th century, when the system of the Romans was revived and a good many treatises were published on the subject. Among the voluminous writings of Roger Bacon is a tractate De Arte ilemoratira, which exists in MS. at Oxford. Raymond Lully devoted special attention to mnemonics in connexion with his ars generedis. The first important modification of the method of the Romans was that invented by Conrad Celtes, German poet, who, in his Epitoma in utramque Ciceroni. rhetoricam CUM arte memorativa nova (1 4 92), instead of places made use of the letters of the alphabet. About the end of the 15th century Petrus de Ravenna awakened such astonishment in Italy by his mnemonic feats that he was believed by many to be a necromancer. His Phamix rtis ..4.1emorix, published at Venice in 1491 in four volumes, went through as many as nine editions, the seventh appearing at Cologne in 1608. An impression equally great was produced about the end of the 16th century by Lambert Schenkel, who taught mnemonics in France, Italy, and Germany, and, although he was denounced as a sorcerer by the university of Louvain, published in 1593 his tractate De Memoria at Douai with the sanction of that celebrated theological faculty. The most complete account of his system is given in two works by his pupil Martin Sommer, published at Venice in 1619. Giordano Bruno, in connexion with his exposition of the ars generalis of Lully, included a memo•ia tecknica in his treatise De Umbris Idearum.

About the middle of the 1 ith century Winckelmann made known what he called the "most fertile secret" in mnemonics, namely the use of letters with figures so as to express numbers by words ; and the philosopher Leibnitz adopted an alphabet very similar to that of Winckelmann in connexion with his scheme for a form of writing common to all languages. Winckehnann's method was modified and supplemented in regard to many details by Richard Grey, who published a Menzori a Technith in 1130. The principal part of Grey's method is briefly this : "To remember anything in history, chronology, geography, Arc., a word is formed, the beginning whereof being the first syllable or syllables of the thing sought, does, by frequent repetition, of course draw after it the latter part, which is so contrived as to give the answer. Thus, in history, the Deluge happened in the year before Christ two thousand three hundred forty-eight ; this is signified by the word Deletok, DA standing for Deluge and etok for 23-18." To assist in retaining the mnemonical words in the memory they were formed into memorial lines. The vowel or consonant which Grey connected with a particular figure was chosen arbitrarily ; but in 1806 Feinaigle, a monk from Salem near Constance, began in Paris to expound a system of mnemonics, one feature of which was to represent the numerical figures by letters chosen on account of some similarity to the figure to be represented or some accidental connexion with it. This alphabet was supplemented by a complicated system of localities and signs, with the aim of expressing, by a more vivid and impressive symbol, ideas which for want of this are apt to pass from the memory, and of establishing between ideas of time same group an intimate relation, so that the mention of the one would suggest the other. Feinaigle, who published a Notice sur la mnemonique at Paris in 1806, came to England in 1811, and in the following year published The Pew Art of Jlemory. A simplified form of Feinaigle's method was published in 1823 by Aime Paris, and the use of symbolic pictures was revived in connexion with the latter by a Pole, Jazwinsky, of whose system an account was published by J. Bern, under the title Exposi General de la Methode Mnemonique Polonaise, perfectionnee a Paris, Paris, 1839. Various other modifications of the systems of Feinaigle and Aime Paris were advocated by subsequent mnemonists, among them being the Phrenotyping or Brain-Printing method of Beniowsky, the Phreno-Mnemotechny of Gouraud, and the Mnemotechnik of Carl Otto, a Dane. The more complicated mnemonic systems have fallen almost into complete disuse ; but methods founded chiefly on the laws of association have been taught with some success in Germany by, among others, Katlic, who is the author of Lehrbuch der Mnenzonik, and Katechisnzus der Gedlichtnisskunst, both of which have gone through several editions ; and in England by Dr. Edward Pick, whose Memory and the Rational Means of Improving it has also obtained a wide circulation. In certain cases mnemonical devices may be found of considerable service ; but all systems which have aimed at completeness have been found rather to puzzle than aid the memory. The fullest history of mnemonics is that given by J. C. F. von Aretin in his Systematische Anleitung zur Theorie and Praxis der Mnemonik, 1810.

MOA. See D NORMS.