KKTA1NKK. 



KETOHT. 



11 



of small 



with a Urp- nt 



id U> h*r I 



.. theai 



of Uic Ulh o. 



martyrdom of 



the ud of the 13th century, the throoe of the 

 ill then uMinlly plaoed t the end of the MM* and 

 thai anything riling above the altar would have 

 1 of the iBtmf^gV" At fint the ratable wa* 

 .1 figure! placed in 



15th century reUbles, whether of marble, (tone, 

 > of large an*, and adorned with a profusion of 

 j the 1-e.t .til|>tunl art of the period. In Her- 

 f were often of extravagant height and costliness, 

 lie al roof, and covered with a multitude 

 own country they sometimes extended quite 

 L The I lading evenU of the live* of the saint to 

 u dsdiralert were now often reprewnted, the carved 

 and the ground gilt : characteristic example* 

 li Kensington Miucum, in one of French work 

 Mr of Agora* in high relief, of about 1500 ; and one 

 the Uttrr |rt uf the 15th century of Flemish work, 

 1 brought frum the cathedral of St. Bavou, Ghent; 

 ffttttn^tm i* a ntill inure remarkable triptych retable 

 rni.in work, in which the life and 

 Margaret are represented by numerous small figure* 

 artaienU, which i : tin- original colour 



nl other retable* of mediaeval date are in the some 

 > one or two in marble of Italian renaissance work. 

 and triptych retablee were much used in the 16th 

 aome very beautiful specimens in ivory and in enamel 

 naington. Many of the churche* of the continent 

 le* uf medieval retablee; and many fine reredoses, 

 e wa* here called, may be seen, more or less muti- 

 irches, as at Durbuu, (iloucortcr, and 

 , St. Albans Abbey Church, Henry Yil.'a Chapel, 

 v. Si. Saviour's, Southward. 



AT-LAW.] 



KETAIMNti WALL u the term uad for a wall erected to resist 

 the thrust of a mi of earth, or of a volume of water stored in a 

 lesoTuif. In consequence of the variable nature of the materials to be 

 sustained, a* well a* of the materials of which the walls themselves are 

 oom posed, the practical application of the mechanical laws usually 

 adopted for calculating the thicknesses of this class of works U more 

 empirical than is usually the case in tho ordinary operations of building. 

 The following are, however, some of the generally received principles 

 adopted by engineers in the construction of these walls. 



>avier, who has applied the higher analysis to the investigation of 

 the laws of the stability of buildings, gives a formula for the thickness 

 of retaining walls, and a table of the weights of the materials com- 

 monly dealt with. The table U an follow*, in English weights and 

 dimensions : 





Material 



YtftUbl* earth, per jrard, tube 



.. 



Clay 



Stiff *rth, with [W!>UM 

 Marl 

 Mod 



Tiff try land 

 Wet ditto 

 AnrUlaeroM Mad 

 ft riTw und 





2SS2 



2GS8 

 1192 

 8847 



leas 



3773 

 2313 

 3193 

 2940 

 8034 

 3380 

 4636 

 3024 



The formula for walls with two vertical faces is ; vailing 

 *, the thickness sought, in yards and decimals, 

 A, the height of the wall above its base, in yards, 

 r, the weight per yard cube of the wall, 

 r', the weight of the earth or other material, 

 t, the angle that material, if left free, would form with the 

 vertical line passing through the foot of the slope ; 





9 IT" 

 0-59 A tangent A/ 



This i"jninl.i would give thicknesses considerably less than th... 

 usually adopted in practice ; for the general rule adopted by engineers 

 is to make tho thickness of retaining walls equal, on tho average, to 

 1 -3rd of the height, or 0'33 A. It must, however, bo borne in mind, 

 that there is no allowance made in the formula for the numerous 

 disturbing causes which are frequently met with, ouch as the subsi- 

 dence of the ground ; nor does it take into account the cohesion of 

 the earth, nor that of the masonry ; it in, in fact, only founded upon 

 



even d**inbte in addition to the extra thickness thus given in practice 

 to the walls, beyond that which is required by the strict application of 

 theoretical laws, to give a batter to tho external faces equal to 1 -:Mth 

 of the bright. A greater batter than this would be objectionable, 

 on account of its catching and retaining the falling rain ; and it i.t 

 desirable that the internal face of the wall should be formed in such a 

 manner as not to hold up any water which might filter through the 



earth piled against it In most; cases, also, the resistance of retaining 

 walls is increased by the introduction of counterforts; especially when 

 the length of the embankment, or earthwork, to be retained is con- 

 siderable. 



Retaining walls used in situations where the earth at their backs U 

 liable to become saturated with water by tidal action, or by the 

 capillary attraction of the earth, must be established on the supposition 

 that their backing become* in fact a semi-fluid, denser than water, and 

 which consequently ha* no angle of repose. Careful observations on the 

 state of the walls in the French ports on the Channel, have shown 

 that in many cases those walls have yielded when their mean thickness 

 has even been as much as (HI : VOO; and it therefore would appear 

 that in such cases it is not safe to keep the ratio of the mean thick- 

 ness below 0-45 or 0*20 to TOO. In reservoir walls of masonry, tho 

 thickness should be made, practically, double that of ordinary earth- 

 retaining walls, as indicated by theory; and especial care should 

 be token to ensure the adhesion of the wall to its foundations ; for it is 

 found that the expression of the resistance of these walls to overthrow 

 is ii' II A, while that of the rebalance to longitudinal displacement in 

 The summit of the retaining wall of a reservoir should bo 

 made at least equal to l-3rd or 1-lth of the head of water ; and the 

 effect of the surcharge of the masonry above the water-line may be 

 neglected in estimating the statical resistance. 



The reader who would desire to study the strict theory of this 

 question would do well to examine the 'Mumoires' by Coulomb, 

 1, ami I'rony, ' Sur la Pouasde des Terres ; ' Navier's ' Lecons de 

 ;ni<|ue;' I'osley's ' Course of Military Instruction;' Moseley'n 

 ' Engineering and Architecture ; ' but the most condensed and practical 

 notice upon the subject is to be found in Carr'a invaluable ' Synopsis 

 of Practical Philosophy,' under the head ' Earth.' The following table 

 of the angle formed by the natural slope uf the materials enumerated 

 may be found useful in applying Navier's formula, previously given, 

 when it may be desired to calculate the resistance of a wall rather 

 more closely than it is found necessary to do in practice : 



1. Fine dry sand forms with the vertical line a slope, 

 having an angle of 69 ; sometimes the angle is, 

 however, 654, when the sand has been well 

 rammed. 



_'. Vegetable earth do. of 554 



3. Loose shingle do. of 61" 



4. Ordinary earth, well dried and pulverised forms 



an angle of 48!"' 



5. Rubble, small and rough do. of 371 



6. Do. do. slight'y moistened do. of 86 



7. Densest and most compact sand do. of 35* 



From this table it appears that 9 usually ranges between 35 and 

 70 ; for water and for extremely fluid mud 6 becomes = 9". 

 RETARDATION. [AoOBUBAtlO*.] 



RETI'CULUS, or RETICULUM RHuMBOIDA'LE (the rhomboidal 

 network formerly used to divide the field of a telescope), a southern 

 constellation of Lacaillc, situated directly between the great stars of 

 Argo and Eridauua. 



No. in Catalogue 



No. in Catalogue of British 



Character. of Lacaillc. Association. Magnitude'. 



ft lii'ii 1197 4 



o . 329 1338 8 



RETINAPHTHA. 



RETINOLE. 



RETINYL. 



RETISTEREX E. A name given by Dumas to inetanaphthaliue. 



RETORT, a chemical vessel in which distillation or decomposition 

 is effected by the application of heat ; for different purposes retorts are 

 made of glass, earthenware, and metal. 



Glass retort* are usually of the annexed form, with a receiver 



Klg. 2. 



Fig. 3. 



attached ; they may be employed for the preparation of such products 

 as do not require any extraordinary degree of cold for the condensa- 

 tion of their vapour: such a liquid is nitric acid. In this cut a 

 represents the body of the retort, b tho neck, and c is the receiver- 



