lS-12.] 



Tin^ CIVIL ENGINKKK AND ARrilTTECTS JOURNAL. 



53 



INSTRUCTION IX DESIGN, AND SCHOOLS IN THE SEVENTEENTH 

 AND EICIITEENTII CENTURY. 



Great as tlic outcry has liccn of late with regard to scliools of design, 

 the plan is liy no means new to the metropolis. At the latter end of the 

 scvcnteentli centurj', while what we may call the mediaiiical portion of art 

 was still llourishing. the symptoms of decay were apparent ; and a little later, 

 the general introduction of coinpo.-ition ornaments c.iusod a rapid decline. 

 The foundation of the school of drawing in Clirist's Hospital is perhaps the 

 first instance of the recognition of de>ign as an essential part of useful edu- 

 cation ; and it is surprising tli.it it had not a more extensive influence, .\liout 

 tlie commencement of the oightecutli century, when Strj-pe puhlishcd his 

 edition of Slow's Survey, the overthrow of the lower branches of art may be 

 considered as complete ; ami we find Mr. 15. Lens exerting liimsclf to 

 produce a better state of affairs. His arguments, published by Strype, arc 

 quite identical with those which have been lately urged; and it will perhaps 

 afford some gratification to extract at length Str\-pe's account of his school, 

 (vol. I. p. 1 73.) 



" Another school for drawing, limning, and painting, set up anno 1077, by 

 one Mr. II. Lens, now or late living in Fleet-street, an art exceedingly useful 

 for all sorts of people, .is for gentlemen that travel, * * and for trailesuien ; 

 such as arc concerned in buililing, as masons, carpenters, joiners, painters, 

 and the like. The professor of this art teachcth on Tuesdays, Thursdays, 

 and Saturdays, in the morning from 8 to 11, and on Mondays, Wednesdays, 

 and Fridays, in the evening, from C to ; the price, a guinea entrance, and a 

 guinea a month. * * He bath very well set forth the general usefulness of this 

 art by a printed paper, which may deserve to be here inserted. Craphice, by 

 .\ristotlc is generally taken for the art of drawing anything (FpacfiiKe) 

 whatsoever, with the pen or pencil, and was reckoned aiuong the cliiefcst of 

 those Ills waiSfvfiaTtt, or generous practices of youth, as renilering them so 

 many ways serviceable to their country, and profitable to themselves. Of 

 incredible service and advantage it would be to our smiths of all sorts, 

 masons, bricklayers, carpenters, joiners, carvers, turners, embroiderers, tapes- 

 try-workers, siUersniiths, jewellers, nay, to all our handicrafts in general. 

 For, show most of the workmen abovcsaid a draught of what you would 

 have ilone, their want of skill in drawing renders it almost useless to them. 

 For example, should an engineer invent a machine, and draw it in all its 

 parts, with its views per front and sides, the whole iu perspective, a ground- 

 plot thereof, with a scale annexed thereto ; with what dilliculty do they 

 work, and the projector must be always by, or all will be marred : whereas, 

 could our handicrafts and mech.inics draw, a man might send his work from 

 a hundreil miles' distance, drawn as abovesaid, ami be satisfieil it wouhl be 

 performed to his mind, and .'according to his directions, ily what has been 

 said, I would not have it thought that none of our handicrafts and mechanics 

 can draw, for some do. of my knowledge, very well ; which qualification hath 

 made them the most excellent of all others, for the best draughtsman will be 

 the best artist, in what art soever. The design of this school is to have a 

 constant nursery or breed of youths proper for artificers. * * For proof of 

 what hath been said, discourse with the meanest of all our handicrafts, though 

 he cannot draw, yet will endeavour to chalk out, after his fashion, your 

 meaning and his ; knowing by pure instinct, that all the rhetoric in the world 

 cannot convince like a drawing. * * If parents sent their rhildren to 

 drawing, as customarily they do to Latin ami writing, it being altogether as 

 useful to them, they wouhl soon find the advantage themselves, and their 

 children would reap thereby; for a master would take ;i servant qualified with 

 drawing with half the money, and be a gainer thereby, for the boy would 

 come to work in half the time." * * 



That Mr. Lens's intention was a good one, there can be no doubt ; but 

 whether in making i charge of twelve guineas a year he made his school 

 acceptable to the working classes, ailmits of great question. As being a 

 l.ibourer in the cause of public instruction, he is, ueterthelcss, entitled to 

 much praise, although the time was so unfavourable to a successful issue of 

 his attempt. .Mr. Uuis was also a private teacher, and afterwards became 

 drawing master in Christ's Hospital. 



OBSERVATIONS UPON THE COMPARATIVE ADVANTAGES AND 



iNtONvi;sii:N(i:s of the employment of ikon wire, 



OR BAR IKON. IN Till; CONSTUUtmON OF SUSPENSION 

 BRIDGES OF GREAT SPAN. 



Ily M. Lk Bi.axc, Chief Engineer of Bridges and Roads. 



(Tranxlatnlfram the t'rench.J* 



Cables of iron wire, and chains composed of bars of wrought iron, miy 

 be compared with reference to their economy and their durability. 



.\s regards economy, the <|uestion scarcely lle^cr^cs discussion, ami it U 

 easy to prove « priuri that, in all possible cases, iron wire liaa the advantage 

 over wrought iron. 



In fact, the Council of the Punts el C/iauiera has adopted the principle, 

 th.it cables of iron wire should be submitted to a tension of \2 kilogrammes 

 (JCJ lb.) per square millimetre (-UUli; square inches) of section; but for bar 

 iron, it was decided that the maximum of tension iUall not exceed n kilo- 

 grammes (17'G lb. nearlyl. 



This principle is founded upon the comparative resistances of iron wire, 

 No. IS, ordinarily employed in the construction of cables, and of iron bars 3 

 to G ccntrimetrcs (1-2 to 21 inches) in diameter. 



The natural consequence of this principle is, that the section of a chain 

 should be greater by one half than that of a cable, for the same tension ; 

 this involves a proportional increase of its weight. In cables of iron wire no 

 joints are used, or at most, but a single one, as in the bridge of Argcntat, 

 and this joint made up of two sm.iU eyes, weighs but little^on the contrary, 

 they are numerous in chains, and where the system is rather complicated, as 

 1 shall prove it should be in bridges of great span, each one of these joints 

 weighs at least 1 tO kilogrammes (309 lb.). On the supposition that the 

 suspension rods are 1'2 metre apart (47] inches), as there is a joint for each 

 rod, there will be 233 kilogrammes (jlllb nearly) for a bridge of 180 

 metres (590 ft.) span. This additional weight, together with that of the 

 bars themselves, which, as we have just seen, is one half greater than that of 

 the cables, produces an excess of tension which must again be resisteil, 

 whence there arises a new increase of section, and consequently of weight in 

 the chains. In applying these principles to individual cases, it is found that 

 the weight of the unit of length of a system of chains exceeds double that of 

 a system of cubles.t Now, as the price of iron wire is once and a half that of 

 bar iron, it is plain that the use of iron wire is more economical than that of 

 wrought iron. 



1 have proved that the total tension is much greater when chains are used, 

 it follows that greater strength must be given to the moorings and to the 

 intermeiliate piers, when the bridges have several openings or bays — a new 

 cause of increase of expense.* 



It appears to us to li.ivc been thus thoroughly proved, that in regard to 

 economy, the cables of iron wire are superior to chains of wrought iron. 



Let us now compare the two systems in relation to their durability. 



The principal objections which have been made to the employment of iron 

 wires are the following : 



1 at. They otTcr greater chances for rapiil oxidation. 



2nd. The imperfection of the jtrcsent process for manufacturing the rabies 

 does not allow us to give an equal tension to all the wires, so that when the 

 cables are raised to their places, the wires which arc under most tension 

 have to support many pounds in excess — while those under least tension do 

 not draw at all. 



* We arc indebted fur the tninslation to the American Railroad Journal. — 

 Kditor. 



I In the rnmparalive iiroposnls which I presenleil for the bridge of Korhe 

 liernard, 1 showed tluit these « eights are in the pro|>orliun of II to 'ii ; in 

 order to replace 11 kilognimniis (2Hb.) of irun wire, uhicli at I f . .'lOe. rost 

 lli francs, M cen., we must employ 2.'i kih gramrnvs (55 lb.) of Hrouxht iron 

 wiih 2'> francs. 



; In bridges of several Inys the cables or chains kliouM be flxrd to the 

 inlernu-diate piers, in order lo avoiil the great changes of form which result 

 friun une<pial loads upon the two bays, if the chains and cables can shdc 

 freely over the lop of the piers. Boc.iuse these [irn h.ivc to rajsl oidy the 

 dillereuce nf the tractions produrol by illfTerent .iddilional loads iipun the 

 two Inys, it would app.'nr at first sight a m.ttier of IndifTerence whether the 

 jierTnanent load.s wliirli .ire in |.<piililirio .ire greater or leu: iievrrllielr.s.1 it is 

 plain that ihe less these permanent loads nre, the Ivtier the piers are in 

 rimdiliiin tii resist the maximum lo.id of <me bay, the other Ix-ing Heslniyed . 

 it is, then, not unimportant that we diminish the [lermancnl load as much as 

 ivslible. 



