to (irive the " animiil siiirits " hither and thither in the brain, till they encounter the trace of the idea it wishes to recall. But, besides the cerebral traces, there are also, according to Descartes, vestiges left in thought itself. Leibnitz located the trace in the monad of the soul anil conceived of it as becoming vanishingly small, but never equal to zero. For others again, the trace is entirely material. Some even go so far as to locate each image in a special ganglion cell of the cortex. On account of its definite character and piclviresqucness, this theory has found many pop- ular expositions. But there are facts that seem to make it untcnalile. For instance, disturbances of vis- ion caused by unilateral lesion in one visual area of the cortex of a dog, wear off after about six weeks. This was explained by supposing that new memory images are deposited in the surrounding area. But it was shown by Loeb, that when dogs are kept in complete darkness after tlie operation (so that the acquisition of new visual images would be impossible) , on being re- leased after a period of six weeks, they are, neverthe- less, entirely normal (Loeb, op. cit. infra, xvii).
More recently, it has been maintained (Robertson, "Sur la dynamique du Systeme nerveux etc.", 438), that the trace is a chemical condition left in the brain by the passing activity of the original impression. This contention is not pure speculation, but is based upon experiments which aim to show that sensory processes are connected with the liberation of acids in the cerebral tissues. This leads to the assumption that " the extent of the memory-trace is proportional to the amoimt of material transformed in a self- catalysed chemical reaction, that tlie number of syl- lables memorized must be connected with the number of repetitions (or time of learning) according to the fol- lowing function: Log. n=Kr + b; where 71 is the num- ber of syllables memorized, r is the number of repeti- tions, and k and b are constants (that is, do not vary when » and r vary) " ("Monist", 1909, XIX, 3S3). The quantity n also corresponds to the amount of substance transformed in the chemical reaction, and r to the time during which it goes on. Calculations based on this equation, compared with observed results, gave very small percentages of error: 0-46 per cent, to 2-5 per cent. Such results seem to indicate that the term "sensory trace" will eventually receive a definite ex-
Elanation, but they are far from affording us the asis of a complete explanation of memory. The in- sufficiency lies in the fundamental defect of all mate- rialistic theories. They fall short of that which they start out to explain: the conscious processes of memory. It is not sufficient to show that there are cerebral traces. This has long been a priori evident, and it is to be supposed tliat such traces will obey a definite law. Over and above this, a complete theory of memory must show how these cerebral traces recall definite conscious processes. This problem remains unsolved. In our haste to find some solution we must neither deny, with the mate- rialist, the first facts known to us, our conscious pro- cesses, nor with the idealist refuse to allow one of the primary deductions from these facts, an external something that gives rise to our sensations. Scholas- tic philosophy has always recognized the fact of man's dual nature — a fact which must be taken ac- count of in any theory of memory. St. Thomas pos- tulated the existence of physiological traces in the organism. But he also pointed out that there must be some kind of residue of the ideas left in the soul itself. Since the ideas are but acts of intelligence, and not intelligent substances — transient activities of the soul itself — and not complete beings on which the mind fums its gaze, they can only live on, as dynamic traces in the passive intellect, awaiting the time when they will exert their influence on some future process of thought — apparently rising from the depths of consciousness, in the act of memory.
The function of memory is further significant as evidence for the substantial nature of the soul. Since ideas are transient processes, there must be a perma- nent something in the mind to account for their reten- tion and reappearance ; and since they are recognized as ideas that were formerly in consciousness there must be something that identifies them and that consequently persists during their absence from con- sciousness (see Soul). The attempt to explain re- tention by means of psychical disjiositions distinct from cerebral traces, is oiniously futile unless it postulates a substance of mind in which such disposi- tions are preserved.
St. Thomas Aquinas. I, Q. Ixxviii, a. 4; Ixxix, a, vi-vii; Bx- posiiio in librum Aristotclis De Memoria et Rcniiniscenlia; DuBRAY, The Theory of Psychical Dispositions, Diss. ("Washing- ton, 1905); LoBslEN, Experimentelle Vntersuchungen iiber die Gedachtnissentwickclung bei Schulkindem in Zeitschrift fiir Psychol. (1902), XXVII, 34-76: 'Loeb, Comparative Physiology of the Brain (New York, 1900); Meumann. Vorlesungen zur Ein- i'thrung in die experimentelle Padagogik (2 vols., Leipzig, 1907); Netschajeff, Experimentelle Vntersuchungen iiber die Gediicht- nissentwickelung bei Schulkindem in Zeitschrift fiir PsyehoL (1900), XXIV, 321-351; Ribot, io Psyehologie des Sentiments (3rd ed., Paris, 1899), ch. xi; Robertson, Sur la dynamique chimique du susthne nerveux central in Arch, intematwnales de physiologic (1908), VI, 388-454; A Biochemical Conception of the Phenomena of Memory and Sensation in The Monist (1909), XIX, 367-386; Steepens, Experimentelle BeitrUge zur Lehre vom okonomischen Lemen. Diss. (Gottingen. Leipzig, 1900); Titchener, Affective Memory in Philos. Review (1895), IV, 65-76; Watt. Experimentelle Beitrage zu einer Theorie des Denkens in Archiv. fur die Ges. Psychol. (1905), IV, 289-436.
Thomas V. Moore.
Memphis, ancient capital of Egypt; diocese of the province of Arcadia or Heptanomos, suffragan of Oxyrynchus. Memphis was called in Egyptian Men- nophir, "the good place". This name, at first re- served to the pyramid of Pharaoh Pepi I (sixth dy- nasty) afterward passed to the siu-rounding quarter, then to the whole city. The Egyptian inscriptions give it other names, several of which properly indicate quarters of the city. It is called Ancb or Aneb-u, "the city of the wall" or "of the walls"; Aneb-hadj, "the white wall", an appellation properly signifying the citadel (Herodotus, III, 91); Ha-ka-Ptah, "the dwelling of the person of Ptah ", an expression first ap- plied to the temple of Ptah, then to the city and which according to certain authors became in the Greek tongue Ai-yviTTos, Egypt; ICha-nofer, "the good crown"; Khu-to-ui, the " light of the two countries", i. e. of Upper and Lower Egypt; Ha-ka-knum-nuteru, "the house of the worship of the divine architects"; Ma-kha-to-ui, "the balance of the two countries", i. e. the dividing point between Upper and Lower Egypt. Memphis is considered to have been founded by Menes, a native of Thini (Herodotus, 11,99; Diod. Sic, I, 50, 51, 67). It was the capital of several dynasties (third, fourth, sixth, eighth, twenty-fourth). It was ■ after Thebes, says Brugsch, the city " concerning which the epigraphical monuments and the papyri have most to teach us". Memphis is often mentioned in the Bible under the name of Mof or Nof (Osee, ix, 6; Is., xix, 13; Jer., ii, 16; xlvi, 14, 19; Ezech., xxx, 13, 16). The Prophets predicted in strong terms the de- struction of this city, and the prophecies were so well fulfilled that the scholars of the French expedition could scarcely discover the true site of Memphis. Memphis has often, but incorrectly, been identified with the ancient Cairo, the Babylon of Egypt. It is now certain that Memphis extended into the plain where stand the villages of Bedrashen and Mit-Rahi- net, on the west bank of the Nile, about twelve and a half miles from Cairo. Its size must have been con- siderable. In this plain are sometimes exhumed colossal statues like that of Ramcses II ; but there re- mains none of the monuments of Memphis unless we except the neighbouring tombs of Saqf|arah, where its inhabitants were formerly buried. Linant Pacha re- covered the great dike built by the founder Menes to turn aside the course of the Nile; this must be the