1 BER 24. 1918] 



SATURE 



O/ 



A step of iIt highesi practical^ and 



■ ticailj «as the publication in 1078, bj R 

 Hooke, an Englishma ti genius but un- 



mperameni . - mpirical law thai 



onal to strain. 4 Then in [680 

 Mark i; s, oven '1 1 [ooke's law, 



indicated thai th 



i thrusl on the othei p 



1. ( 'ouloni ientifically obtained 



quilibrium b) resolving horizoi 

 ion and equating the m 



of the 



In 1807 Thomas Young'' defined thi 



- modulus epo< h-makin 



ced inti 

 ning. Arthur Schuster says thai Young was 

 to I .eonardo da Vinci, the mosl versa- 

 md Helmholtz said thai he was 

 mosl li ar-sighted men thai <a er li\ 1 d. 



Early Practical I ■ 

 In the latter half of the eighteenth centun 



stinguished engineers and architects concerned in 

 ructing a bridge over the Seim and the Pan 

 or Church of St. Genevieve al Paris, finding the need 

 for information, built testing machines of 20 to too 

 tons capacity. Among them were Perronet," Ronde- 

 . ruthei , ' and Girai 

 In 1817 ■ lovi published an 1 ssaj on the 



gth of timber and other materials founded on 

 .it Wuulv. ii h. In i.vs Navii 1 

 with the construction of a suspension bridge at Paris, 



■ .1 all the memb 



load of to tons « ei 1 



with loads up to 70 tons. Navier had also 

 mad. ance in theory in fii si in 



the gi tions ol equilibrium of an • 



It will be alreadv clear that knowledge of materials 

 was i ilong two independent lines— thai of 



experiment and that of analysis. In the latter half 

 of the eighteenth centurj mathematicians of the 

 highesi rank were applying themselves to the pro- 

 blems presented bj thi ind deformation of 



lodies. Bui mathematics is a kind of mill t li- ■ 

 product of which the data with which it 



i< fed. While experimental data were wanting, then 

 were en irs and misunderstandings in the theoretical 

 fnvestigation of elasticity. Prof. Love 1 ' says that in 



"the fruit of all the ingenuity expended by 



mathematicians on elastic problems might be summed 



up as an inadequate theor) of flexu 1 qneous 



theon of torsion, an improved theon of the vibrations 



iars, and thi definition of Young's modulus." 



Rut p - had at this time accumulated 



empirical knowledge of the resistance of 



materials No oni can overrate the importance to the 



thi oretical 1 es< ai ches n applii d mechanics. 



bur that branch of science is outside the purposi of 



this lecture. 



siderabte advances in knowledge of strength of 



made b\ Eaton Hodgkinson, who, 



though largely self-taught, had considerable mathe- 



* I'e potentb restil'itiva." (London. 1678.) 



5 " F.ssr.i ^ir une application des regies de nisximis et minimis, 

 par divers sarani, 1776. 



* •" Lecture- on Natural Philosophy and the Mechanical Arts." Lecture 



I Le-aje, "2nd Recuel de Memoires drs Ponts et Chaussees." >3o?. 



p. IS'. 



- ,:e I'.-.rt de batir." 6th e 

 vres Je Gauthey," looq, p. 269 ; fotirn 



nalvt'que de la resistance des so T i<i.j 



II " Notice sur te pom des Inva'ide«," p. 2S4. 

 " "Treatise on the The.ny of Elasticity. '» . 



. 2556, VOL. 102" 



in.' pi ei I-- 

 position of the neutral axis of the cro — action of a 



rated in a paper 

 on trans ngth of materials in 



1822." Between 1X47 and 1853 h 



n< 1 ring at Univi 1 n • 



irried oul the well-known experiments on tin 

 cas I in 1840 



and 1857 ' In- publishei 



olumns which form the basis , j 

 siill in us.-. Though ! wa~ 



rough, h< so designed I - were 



accui 1 il limit of error. 



The Conway and Menai Hr,.i. 



A g ' • arose out of th.- circum 



attending the construction of the Menai and Conway 

 tubular bridges. A railwaj had to be carried 

 spans not before accomplished for such work. Robert 

 henson imagined a suspension bridge with plat- 

 form stiffened tn wrought-iron girders, and then 

 siill exist in the piers of the Menai Bridj 

 mints for supporting chains. Early, however, Sii 

 \\ - j 1 1 mi T a:!: 1 rn from expeninK with ships, 

 formed tin- opinion that girders would support them- 

 - without chains. Much knowledge was found 

 n. be wanting, and very extensive experiments on a 

 large scalt were carried out in 1845-48, in which 

 Faiibairn, Hodgkinson, and F.dwin Clark assisted, 

 and mair. scientific authorities were consulted. 

 was a great clearing-up of ideas as to the laws of 

 strength, especially in the case of built-up 

 structures, and a- to provision against buckling of 

 members in compression — a fundamental question, as 

 we have learned in the case of the Quebei Bridge 



The most novel expedient was the testing of a 

 Menai Bridge, one-sixth of full si/,-. The 

 model was of 7 - - f t . span and 4; ft. deep. It was 

 broken six times by dead weight, b.-ing repaired where 

 weakest after each fracture. In this way its strength 

 was increased from 355 to Sot tons, or. including 

 iis own weight, from 38 to is,, tons. Hence was 

 deduced a law for geometrically similar tubes, namely, 

 that the strength increased only. as the square of the 

 linear dimensions, but the weight as the cube. It 

 follows that there is a limit of increase of dimensions 

 for a girder of any given type and material at which 

 the stresses due to the weight of the structure become 

 equal to the safe working stress on the material — a 

 limit approached in some modern bridges. 



The Britannia and Conway bridges were successfully 

 completed, and gave rise to tin- tvpes of girder bridges 

 which have prevailed from that lime. But it is 

 interesting that Eaton Hodgkinson almost to the last 

 considered thai suspension chains would be necessary, 

 Edwin Clark states thai with few exceptions 

 scientific men eithei remained neutral 01- ominous!) 

 shook their heads n:d hoped for the he~t. ,r 



]■ ti -, / 0) the Introduction •>! Steel 

 Wrought-iron was ., material of tolerabh uniform 

 qualitv, bin steel varies , in its properties through a 

 wide ran-., and in the earh da\s was sometimes 

 treacherous. Hence came about the demand for much 

 more general and systematic testing. In 1858 Messrs 

 Robert S'apier and Sons proposed to use steel in so 

 high-pressure boilers. Doubtful .1- 10 the auali 

 the so-called homo-. 'neons metal and pud!'' i steel 

 then manufactured, they employed Mr. David Kirkaldy 

 sis which, it is believed under thi 



13 Memoirs of Manchester Philosoph : cal Society 



u MM., vol. v. 



15 Phil. Trans 



i« " Britannia and Com.:. I » in Clark, 1850. 



I" Lcc. cit., vol. i., p. 298. 



