66 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[March, 



brickwork. They are like tlie feeble be ist in the fable, who indued 

 himself with the skin of the lord of the forest. 



Not unfrequently they are prostrated in ruin, the result of their 

 own pretensions. Some of these vile showy structures in the new 

 metropolitan streets have recently failed in this manner. We are 

 not destructionists, but we rejoice greatly at the intelligence. If any 

 one would compare the mere workmanship of plastered and un- 

 plastered houses, let him compare those of Regent-street with the 

 adjacent Hanover-square. In the latter place, the honest homely 

 bricks show themselves plainly, as if they had nothing to be ashamed 

 of. But an honest builder could have taken no pride in his work 

 when "running up" the neighbouring linen-drapers' palaces. Deceit 

 begets dishonesty: a good bricklayer will soon become a bad one 

 when he knows that his work will be concealed by white slime. He 

 has no gratification in doing his work well-he shirks it and cheats 

 his employer. 



To assist the architect in carrying out the system we so strongly 

 advocate, steam has been brought to his aid in rendering the pro- 

 ductions of carved work less costly than when produced by manual 

 labour. It is our intention to direct attention to the merits of such 

 works. We have already noticed the Patent Architectural Carving 

 Works, in Eccleston Street, Pimlico, and explained the machm- 

 ery. The experience of two more years has enabled the proprietors 

 to' adapt the machinery to works that were not originally so pro- 

 duced. In the show-rooms may be seen architectural perforated pan- 

 nelling for gallery fronts, parapets, ceilings, roofs, and wainscotting, 

 lecterns, furniture, church screens, and other works, generally possess- 

 ing the merit of correct design and perfect workmanship. One oi 

 these elegant screens we have shown in an Engraving (Plate VII). 

 It has been lately erected at Great Malvern church, in the archway 

 of the chancel, and is entirely executed in wainscot by the aid of the 

 machinery of the Patent Carving Works, at a very small cost ; its 

 length is IG feet, and height nearly 12 feeU 



The annexed wood engraving (fig. 1) is another happy example of 

 the application of the labours of the same Works ; it shows the truss 

 of an open timber roof, 3'J feet span. There are eight of these 

 trusses, together with the moulded purlins, ridge piece, cornice, 

 rafters, &c., all executed in oak, for Ravensworth Castle dining-room. 

 The roof is 30 feet span, and 70 feet long. 



Another specimen, in a different material (fig. 2), exhibits the head 

 of a window. This was executed in Caen stone, for Carlisle Cathe- 

 dral. 



Fig. 3 is a specimen of inlaid stone paving, which was also exe- 

 cuted by the carving machinery for Great Malvern church. 



The Company have recently executed various other works, among 

 which we may mention the flooring of Sir Robert Peel's Picture Gal- 

 lery, and a beautiful stone screen for St. John's Church, Strati ord, in 

 Essex, which has excited great admiration. 



It will be seen from the drawings we have given, and the prices, 

 that ornamental architectural works, of a highly ornate style, may be 

 produced in real materials, at about the same price as the counterfeit, 

 when we take into consideration the cost of staining or painting, 

 graining, and so forth. Much may be done if the architect will 

 devote his attention to the subject, and get rid of the prejudices 

 which he has been led into by a false education -.-let him well stu.ly 

 protortion. More is produced by this in a public building than al 

 your excrcsences of enrichments, which are too often applied as il 

 the structure were intended to be the show-building of a plasterer 

 or artificial ornament manufacturer. 



NOTCS ON ENGINEERING, 

 No. VII. 



THE FORM AND EQUILIBRIUM OF ARCHES. 



The object of the present paper will be to explain a few theorems 

 respecting the equilibrium of arches, which are very simple, and of 

 great practical importance. They may, however, be prefaced by a 

 notice of the authors who have already written upon the subject. 



It may be considered certain that the medieval architects, notwith- 

 standing their extraordinary skill in constructing arches and flying- 

 buttresses, and in determining the position and dimensions of piers and 

 buttresses, derived their rules from experiment, and not from theory. 

 This opinion rests upon the authority of the most eminent architec- 

 tural writers of the present day, among whom may be cited Professor 

 Willis, who fortunately is able to combine two very diff-erent kmJs of 

 knowledge, which are both necessary for the examination of the sub- 

 iect-archfflology and mechanical philosophy. Parent and De la Hire, 

 who wrote about 150 years ago, seem to have been the first who en- 

 deavoured to give a mechanicaUheory of the arch; and since their 

 time, the number of writers on the same subject has been extremely 

 numerous, and has included some of the most eminent mathematicians 



'"uToutd occupy too much space to notice the labours of these 

 authors, or even to enumerate their works. But a sufficient y distinct 

 notion of them mav be obtained by considering them divided into two 

 distinct classes, who investigated the theory from two altogether diffe- 

 rent points of view. The first class-the earliest and the most nume- 

 rousidirected their attention chiefly to the conditions to which the 

 component stones of an arch must be subjected in order that they may 

 not Blide upon the surfaces of mutual contact. The second class con- 

 sisted of those who neglected this idea of sliding altogether, and con- 

 fined themselves to the conditions necessary to prevent the joints from 

 ovenins The first class includes the names of Couplet, Bernouilh, 

 Belidor, Coulomb and Bossut, continental writers who have 

 been followed by Hooke, Gregory, Hutton, Emerson, Whewell and 

 Gwilt. in this country. Many of these writers have considered the 

 arch as composed of perfectly smooth voussoirs, and sustained inde- 

 pendently of frictiou-in this condition the arch is said to be "equili- 



'"^ Now 'this theory of the arch, though long in vogue and sanctioned 

 by the highest authority, has been found practically insufficient for the 

 purposes of the engineer. As a matter of fact, the voussoirs of 

 Lhes have always so great friction that they never slide upon each 

 other. The old theory, therefore, speculated about an accident which 

 experience showed to be never likely to occur. Consequently the 

 investigations, though frequently exhibiting extraordinary mathemati- 

 cal research, and leading to very beautiful results, con d scarcely be of 

 any direct value to the practical engineer; anU accordingly, a wri er 

 who has taken the highest position in this country for his pra tic 

 rpplications of mechanical principles-Professor Moseley, has in h s 

 writings entirely excluded the speculative investigations just men- 

 U ned:and has confined his attention to the statical conditions ne es- 

 sary for preventing that accident which may and does occur-the 



''tZ:^J^'^ endeavour to follow him. It hasunfo.u- 

 nitelv happened that though his principles are characterised by ex- 

 ue ne accuracy, the results are frequently ^°^ -^-^^^f ^ ^^^, 

 value to an engineer. Now what will be here attempted, i, to estab- 

 U ha few general propositions which are frequently unknown or mis- 

 I ed,"fd to give soma methods by which the form and thrust o 

 a ehes niay be calculated,-not with anything like the genera hty and 

 urecision studied by Professor Moseley, but with accuracy quite suffi- 

 ^ienl T'ordinary purposes, and with perfect facility of computaUon 

 to all who are acquainted vfith common arithmetic. 



