RETAINING WALLS. 69 destructive tendencies. The diiriculty of doing tliis arises from the fact that the pressures ex- erted l>y the vedge-shai)cd mass of earth vary so greatly with the character and physical condi- tion of the material that they can onlj- be rough- ly apiiruximated. Kngineers have worked out numerous formulas for calculating the dimen- sions of retaining walls, which are designed to ine'^t the varying conditions of the load, but these formulas have to be based on so many hypotheses that their jjractical value, except for general indications, is quite limited. The greatest difficulty arises from the action of water, which accumulates behind the wall and may transform the earth to a semi-lluid state, thus enormously increasing its pressure, and one of the chief desiderata in rctaining-wall con- struction is that this water shall be kept drained away. This is usually accomplished by having drainage holes, commonly called "weep holes,' through the wall at intervals, by means of which the water runs off as fast as it accumulates. Retaining walls are generally made trapezoi- dal in section, as shown by the diagram, but they are also built with rectangular sections and with ' concave faces. Danger from crushing seldom exists exce])t in very high walls, and danger from shifting can be easily avoided by laying the masonry with its courses dip])ing slightly from the front toward the rear. Careful work- manship and perfect drainage are the essentials of good retaining-wall construction. BiBLioGB.PHY. For a discussion of the theory of retaining-wall construction for various forms of walls and various conditions of loading, consult : Howe, Rctitining Walls for Earth (New York, 1896) ; Merriman. Retaining Walls and Masonry Dams (Xew York, lSn2); Cain, Practical De- signing of Retaining Walls (Xew Y'ork. 1888) ; and Baker. Treatise on Masonry Construction (Xew York, 1900). See IVIasonky. RETALIATION (from Lat. rrfaliare. to re- taliate, from re-, back again, anew + talis. such I . Properly, the return of like for like; usually, the infliction upon a wrong-doer of an evil similar to that which he has wrought. In early law, when wrongs are redressed by the act of the injured party or kinship group, such re- dress often takes the form of retaliation. The retaliatory idea sometimes assumes peculiar forms: as when the man whose father lias been slain seeks to slay in return not the offender himself, but the offender's father. The clearest ex- pression of the lex talionis. or law of retaliation, is found in the Jewish rules, "An eye for an eye and a tooth for a tooth," and "Whoso sheddcth man's blood, by man's hand shall his blood bo shed." In the" Roman XII, Tables talio is au- thorized as a penalty for mayhem (niembrum ruptum) if the injured party refuses to accept pecuniary compensation. Retaliation is sanc- tioned in the Visigothic laws, but this (accord- ing to Brunner. who asserts that there is prac- tically no retaliatory element in old German law) was d>ie to the influence of the Old Testa- ment. A modern parallel was afforded in colo- nial Connecticut, where the penalty of castration was imposed in at least one instance on the au- thority of the llosaic rule. ^Vhen public punishment begins to take the place of private vengeance, penalty may be, and often is, measured according to the degree of RETENTION. wrath which the offense commonly urouses. but purely retaliatory penalties lend "to disa|>|)ear. To punish a perjurer by hewing olT the haml which he lias raised in swearing, or u slanderer by cutting out the tongue, is not properly re- taliation. Such penalties may originate "in a sort of personification of the offending nienilier, or they may be based, as Urunner suggests, on the desire to make the relation of crime and punishment obvious: "the penalty itself is to declare why it is inipo.sed." Retaliation may lie based, in part, on tiiis idea, but such synifxilic penalties are not in themselves retaliatory. More closely akin to retaliation is the inlliclion upon a false accuser of the penalty which would have been inflicted on the accused if the charge had been sustained. The term retaliation is sometimes loosely em- ployed to describe the return of evil for evil even when there is no similarity between the otfeiisc and the punishment. In this broad .sense, retali- ation includes all extra-legal vengeance and all leg:il punislunent. It is in this sense that we speak of 'the retaliatory theory' of punishment, meaning the theory which bases the right of the community to punish criminals on the fad that they have injured the community by their crimes. RETBERG, rSfberK, Ralf von (1812-85). A German writer on art. born at Lisbon, where his father was then stationed as a captain in the German-English Legion. From 1829 to 184.5 Ret- berg served as an officer in the Hanover Army, and then settled in JIunich. His works are of especial value for the knowledge of art and culture at Xuremberg, and include: Niirnbcrgcr Briefe r»r Geschichte der Kunst (1846) ; iim- hcrgs Kunstleben in seincn Dcnkmalcn (1854); Kulturgcschichtliche liriefe (186.')); Albrerhl Diirers Kupferstiche and Hohschnittc, kriti.'iclws Verzeichnis (1871). Postluimously. Die Ge- schichte der dcutschen WappcnhihUr (Vienna, 1888) was published from his manuscripts. RETENTION (Lat. retentio, from retinere, to retain, hold back), or Conservation. In psychology, the effect which is left upon the organism by psychophysical processes. One is said to retain one's experiences and to "live them over' again and again. Retention is, therefore, the presupposition of memory. In Herbartian psychology (see Hebbart) ideas are supposed to maintain their existence even after they have left consciousness. But most recent writers on psychology* regard retention as a physical func- tion. It is, they assert, the brain that 'retains.' This view is based partially on the observation of jjathological cases, which reveals the fact that both general and specific disturbances of memory are connected with definite changes either in the cortex as a whole or in some lin;ited area of it. (See Apha.sia.) These pathological facts have told us something of the 'scat' of retention. Lesions in one legion of the cortex affect retention of visual sensations and ideas; lesions in another region, that of auditory sensations and ideas. There is. however, sfill much doubt as to the extent of the differentiation of cerebral functions. Concerning the actual physiological changes which are left over from excitation there is also some difference of opinion, ilost psychologists agree, however, that the activity which a stinuilus pro- duces ceases with the passing of the stinnilation, but that some kind of modification remains.
