92 



NATURE 



[November i6, 191 i 



of Ilis Majesty's dorkyards are mainly staffed by ex-pupils. 

 The outlay for whirh this wonderful return is obtained 

 dof's ni)t t'xcefd 4000/. per annum. 



From the bcj^inninjj tht- Admiralty has insisted on the 

 faithful obstTvanie of two (guiding principles. In the first 

 plate, the apprentices who attend the school do so partly 

 in Admiralty time. At present the five periods a week 

 tire taken, three from the boys' free time and two from 

 .Admiralty time, and Admiralty time spent at the school 

 is paid for. In the second place only those pupils are re- 

 tained who are found to have the requisite ability and 

 industry to profit by the higher instruction ; a continuous 

 process of sifting goes on, and the waste of effort is thus 

 reduced to a minimum. Those pupils who go out com- 

 paratively early find their position on the wage-earning 

 staff ; and, as Sir William White testified, they are 

 altogether different from ordinary workmen, because of 

 the training, short as it may be, which they have had in 

 the school. \\. the same time, there is sufficient material 

 retained for the training of oflicers, who will ultimately 

 fill the higher constructional posts. .A third principle has 

 been rendered possible of application in recent years, and 

 no candidate is now admitted who has not obtained a 

 sound preliminary education. The number of apprentices 

 in attendance is 180 ; and the school is arranged in two 

 sections, which attend on alternate days. The full course 

 extends over four years, but there is a weeding-out process 

 at the end of each year. Of those who complete the 

 course a few are selected by examination from all the 

 dockyards for an advanced three-year course at the Royal 

 Naval College, Greenwich, after which they join the Royal 

 Corps of Naval Constructors. The competition for 

 admission to the dockyards as apprentices is severe, and 

 therefore at the outset a careful selection is possible. 



The late Lord Spencer, when First Lord of the 

 Admiralty, appointed a committee to consider whether the 

 schools might be abandoned in view of the enormous 

 advances which had been made in the provision for 

 elementary education. Happily for the nation the com- 

 mittee's verdict was unanimously in favour of their reten- 

 tion. The development of to-day in the provision of tech- 

 nical instruction is held by some to justify a fresh pro- 

 posal for the abolition of the schools, and the transfer of 

 their pupils to the municipal technical schools of the dock- 

 yard towns. It is to be hoped history will repeat itself 

 and that the schools will be allowed to continue their 

 unique work. .As Prof. Gregory said, they arc at least a 

 generation ahead of most of the other technical institutions 

 •of this country. Their close association with the dockyard 

 has benefited both. Prof. Worthington pointed out how the 

 problems of the dockyard are brought to the schools for 

 solution, and he also dwelt upon the interest and pride 

 which the rank and file of the yards take in the schools. 

 To sacrifice a century-old tradition for the sake of saving 

 a few thousand pounds would be a deplorable mistake, 

 particularly at this juncture, when the .Admiraltv's example 

 will be most valuable to administrators and educationists, 

 who have good reason to be dissatisfied with the condition 

 of technical education in the country generally. 



SOME ENGINEERING PROBLEMS AND THE 

 EDUCATION OF ENGINEERS} 



TT is a consequence of the scientific basis of engineering 

 that it is international, not national. Scientific 

 -advances are not restricted within political boundaries. If 

 we gave the world the steam turbine, Germany returned 

 us the gas engine and Diesel engine. Ability to appreciate 

 the value of new discoveries, and readiness to take 

 advantage of them, depend as much on a widespread 

 scientific education as the making of the discoveries them- 

 selves. 



My^ distinguished predecessor, out of a long and varied 

 experience in the development of the most modern of the 

 many branches of engineering industry, discussed the 

 economic conditions of production on which successful 

 manufacture depends. It will be more natural to me to 

 deal with some of the technical principles on which the 

 successful design of engineering structures is based. 



1 From an address delivered to the Institution of Civil Engineers on 

 November 7 by Dr. W. C. Unwin, F.R.S., president of the Institution. 



NO. 2194, VOL. 88] 



Strength of Materials. 



The object of a study of the strength of materials is t< 

 determine the proper dimensions to be given to par?- ' • 

 mjichines or structures, in order that they may resi- 

 straining actions to which they are subjected wn 

 breaking or prejudicial deformation. It is a modern stud\ 

 for the earlier architects and builders seem to have had r.' 

 definite knowledge; only it may be noted that the <-■<■ 

 buildings were the most massive. The Egyptian col 

 were not more than five or six diameters in height, iv 

 (ireek about nine. .Media-val buildings depend more 01 

 considerations of stability than of strength ; but there ar' 

 medieval columns carrying arches which are twenty-si\ 

 diameters in height. 



So far as we know, however, Galileo (born 1564, di» ' 

 1642) was the first man of science definitely to consid< 

 strength. He found that a rod of copper susp' i 

 vertically might have a length of " 4800 arms," or. 

 yards, before breaking in tension by its own weig!.;- 

 reasonable result. Having no conception of elasticity or 0: 

 variation of stress due to variation of deformation, h' 

 seems to have assumed that bodies always broke h\ 

 tension, and that tension was uniform at the surface <>' 

 fracture. Applying these notions to determine the strengtl 

 of a cantilever, he supposed the whole cross-section woul' 

 be in tension uniformly distributed. He arrived at ai 

 equation for bending strength which for rectangul.i 

 sections is right in form, but affected by an erroneou- 

 constant ; and he acutely deduced the result that, while . 

 model of a structure might be strong enough to carry .• 

 load, the structure itself might be so large as to brea!; 

 by its own weight. This is the germ of the law of : 

 limiting span for bridges. On the same false assumption - 

 Grandi, in 1712, published elegant and correct demonstr.i 

 tions of what we know as solids of uniform resistance (■ 

 bending. It is not the first instance in science of fals- 

 assumptions leading to partially correct results. 



It was not until i6(k) that Robert Hooke discovered tb' 

 fundamental law that stress is proportional to strain ii 

 elastic materials. It was not until 16S0 that anyone mad 

 further experiments on the strength of materials. Thn 

 Mariotte made rough tests of very small bars of wood an 

 glass strained in various ways. He first perceived that i 

 flexure part of the cross-section is in compression and par 

 in tension, and placed the neutral axis for a rectangul.r 

 bar at half the height, correcting Galileo's result. It wn- 

 not until 1776 that Coulomb determined the position of tli 

 neutral axis for simple sections, and not until 1824 th.r 

 Navier determined it for all sections. 



In 1729 Muschenbroek, at Leyden, published the resuli- 

 of what may be considered the first tests of materials mad 

 with precision. He made tension and bending tests, an 

 tests of long columns, but on a very small scale. Perronci 

 occupied with the construction of the Bridge of Neuilly. ii 

 1758 constructed the first comparatively large testing 

 machine, a machine capable of applying a stress of 18 tons. 

 Rondelet, in 1787, constructed a testing-machine with 

 knife-edges, and with a screw arrangement for taking vv 

 the deformation of the test-bar. It was the first machin 

 containing in principle all the essential elements of 

 modern testing-machine. Labardie, soon after, constructed 

 a 100-ton machine for the Port of Havre, and Girard 

 carried out with it the first tests on a large scale of the 

 elasticity of materials. In 1813 and 1817 Brunton and 

 Company and Captain Sam Brown constructed cable-test-, 

 ing machines. 



Theory of Elasticity. 



.\ very great step in the simplification of the math 

 matical expression of formulae of strength of materials wj 

 taken by that very remarkable English physicist Thoma 

 Young (1773-1829). who defined the coefficient of dire 

 elasticity, or Young's modulus, and first considered shea 

 as an elastic strain. The time had come for the develc 

 ment of a general theory of elasticity. Navier, in 182) 

 first investigated the general equations of equilibrium 

 an elastic solid, starting from an assumption as to tl 

 molecular constitution of matter. Navier's equations at 

 still accepted, though part of his reasoning is consider 

 to be unsound. .At the same time, Cauchy founded tt 

 theories of stress and strain, and Lame? and Clapeyro 

 made important developments. 



