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THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[October, 



the receipt of this apply to the London office of the Peninsular nnd Oriental 

 Steam Navigation Company, and yon will receive a tin case, in which are 

 tracings of two taper cliain bridges, with specifications, &c. The one a single 

 curve of 250 feet span, is now erecting, and will shortly be completed." The 

 other, &c. — Again, in same letter — 



" I want your candid opinion on my performances, and do not imagine 

 that it is likely to detract from your employment, my making some here, for 

 the system is now tboroughly established here, and we want so many that in 

 a short time I hope to send you a large order." The bridge of 250 feet 

 span was described in the specification to cross the Bailee Khali, near Cal- 

 cutta. 



A tracing of the drawings and a copy of the specification were made in ray 

 office, and afterwards published in the Mechanics' Magazine for the 19th of 

 October last. Since then nothing has been said of this bridge, nor had I 

 heard a word on the subject until the late Overland Mail brought news of 

 the failure of a suspension bridge across the liallee Khali, near Calcutta, 

 which, as place and dimensions correspond, I presume to be the same, al 

 though I have had as yet no direct information about it. I cannot therefore 

 give you any particulars of the accident, but all the reports agree in ascribing 

 it " to an error of the contractor, which does not in any degree effect the 

 principle upon which the bridge was built." This is so far very satisfactory, 

 though even without it I should not have been at all anxious on the subject, 

 for 1 could in no ways be responsible for errors committed several thousand 

 tuiles oil", especially as I had not at all interferred with the works. 

 I remain, your's, very obediently, 



James Dredge. 



Jialh, September 3, 1S45. 



On tliP whole the main question for consicli-ration seems to be this — 

 wlietlier in a suspension bridge 250 feet long, "iwu liars each If 

 inches in diameter could by any arrangement be made to support and 

 hold the centre with sullicient security. It can scarcely be supposed 

 but that there is some limit, beyond which, if the reduction of the 

 thickness of the central bars be carried, the security of the structure 

 would be endangered. If there be no limit of t)iis kind, then we must 

 come to the conclusion that the bridge might be so constructed that 

 there should be tto tension at the centre; that is, that the bridge 

 might be divided at the centre without falling. In this case the platform 

 instead of a tension or strain, must exert a thrust to keep the chains 

 in tlieir places. 



Thore is one point in Jlr. Dredge's letter which we wish to notice. 

 He says that the centr.d strain " is transferred to and distributed over 

 the whole liorizontal line of the platform." If by the phrase "trans- 

 ferred" be meant that the tension at the centre is lessened or removed, 

 we must with submission call the doctrine in question. 



if A E represent half the platform, E being the centre, and this half 

 F OH 



be acted on by tensions along D F, C G, B H, then by the ordinary 

 rules of statics the horizontal force at E necessary for statical equili- 

 brium is equal to the sum of the horizontal parts of these tensions. To 

 express the same thing analytically, if the oblique tensions be called 

 T, T„ Tj respectively we have, resolving forces horizontallv 



Tension at E = T , cos F D A + T„ cos G C A -f T, cos H B A. 



This is indisputable to the merest tyro in theoretical mechanics; 

 unless, indeed, we suppose parts of platform to exert thrusts instead 

 of tensions, in wliiuh case the statement that the tension is diffused 

 out the platform becomes self-contradicted. 



MODERN GREEK FRESCO PAINTING. 



There are on Mount Athos twenty large monasteries, two hundred 

 and fifty hermitages, and nine hundred and thirty-five churches, 

 chapels and oratories. All these edifices are painted in fresco, and 

 possess pictures on wood. From this source arise the artists of 

 Greece. M. Didron, in his JManuel d'Icoiwgraphie Chrctienue, gives 

 an interesting description of these painters at their work. 



"The first convent which we entered," says he, "was that of 

 Esphigmenou. From the great church just built the scaffolding was 

 not yet removed. A painter of Kares assisted by his brother, two 

 pupils and two apprentices was covering with historical frescos the 

 whole of the inner porch of the nave. I ascended the scaflold on 

 which were the master painter and his assistants, and watched the 

 progress of the work. The brother spread tlie mortar on the wall, 

 the master sketched the picture, the first pupil filled in the lines 



which the master had not time to finish, the younger pupil gilded the 

 glory round the saints' heads and painted the inscriptions and orna- 

 ments, the two otiiers who were younger mixed the colors. The master 

 painted or sketched from memory or inspiration. In one iiour lie 

 traced before our eyes on the wall a painting representing our Saviour 

 giving to his apostles the mission to preach the gospel and baptise. 

 The Christ and the eleven other figures were almost of the natural 

 size; tliey were designed and drawn from memory without any model 

 or rough sketch. While examining the other pictures I asked him 

 if he had executed them also. He replied affirmatively. 



We were astounded, for the paintings were far superior to those of 

 our own second-rate artists who paint religious subjects. The painter 

 astonished me by the powers of his memory; he not only finished his 

 designs without rough sketches of any kind, but 1 heard him dictate 

 to the second pupil the inscriptions and sentences which were to ac- 

 company each picture. He recited without notes or book, and all 

 was rigorously the text of the sentences which I had observed in 

 Attica, in Peloponessus, and at Salamis. I expressed to him my ad- 

 miration, but my surprise greatly astonished him, and he replied with 

 whit 1 thought rare modesty, that it was all very simple— much 

 easier than 1 thought for ; and then he quietly resumed his task." 



HORBURY SCHOOL, 



Near IVakeJield, Yorkshire. 

 The annexed engraving exhibits the construction of the roof, and 

 the design of the end windows of a National School lately erected at 

 Horbury, near Wakefield, under the superintendence of Mr. R. .Sharp, 

 architect. We are indebted to him for several drawings of the build- 

 ings, but we have selected the transverse section as it exhibits the 

 principal features of the construction. The design appears to be a 

 pleasing and satisfactory proof that architectural effect does not neces- 

 sarily involve great expenses. The building cost £800, and the re- 

 petition of the high arched molded ribs throughout the length 



of the interior must necessarily produce considerable effect. The 

 crowns of these arches are 19 feet from the ground, and the springing 

 is from stone corbels let into the walls. The main ribs are 22 feet 

 G inches span and 16 feet apart, and are 12 inches by 8 inches formed 

 in two thicknesses, and intermediate ribs over the windows 10 inches 

 by G inches are also formed in two thicknesses. On each side of the 

 building externally are buttresses which resist the pressure of the roof 

 which is covered with heavy stone slate of the district, and it is proof 

 of the little pressure of the high pointed arches, that though there is 

 scarcely any resistance to the ribs in the windows the work stands re- 

 markably well. The scantling of the timbers is as follows: principals 

 6} inches square, plate 7x5, rafters 3i by 3 inches, thickness of walls 

 2 feet inches, with buttresses 2 feet projection and 2 feet on face. 



