TRANSACTIONS OF SECTION G. 1187 
-am sorry to have no better explanation to offer, but whatever may be the immediate 
-cause of fragility, no doubt exists that it is induced in metals by frequent bendings, 
‘such as a railway bridge undergoes. This fact, however, is not recognised in our 
Board of Trade regulations, which remain as they were in the dark ages, as do 
those of the Ministry of Public Works of France and other countries. With us it 
is simply provided that the stress on an iron bridge must not exceed 5 tons per 
square inch on the effective section of the metal. In France it is still worse, as 
the limiting stress of rather under 4 tons per square inch is estimated upon the 
gross section, regardless of the extent to which the plates may be perforated by 
rivet holes. In neither case is any regard had in the rules to intermittent stresses 
or the flexure of compression members. In Austria the regulations make a small 
provision for these elements; and American specifications make a large one, the 
limiting stresses, instead of being constant at 5 tons, as with us, ranging from about 
24 tons to 63 tons per square inch, according to circumstances. It is hardly 
necessary that I should say more to justify my statement that, as regards the 
admissible intensity of stress on metallic bridges, absolute chaos prevails. 
Engineers must remember that if satisfactory rules are to be framed, they, and 
not Governmental departments, must take the initiative. Informer days the British 
Association did much to direct the attention of engineers to this important matter, 
but, so far as I know, the subject has been dropped for the past twenty years, and I 
have ventured, therefore, to bring it before you again in some detail. Weare here 
avowedly for the advancement of science, and I have not been deterred by the dry- 
ness of the subject from soliciting your attention to a branch of science which is 
‘sadly in need of advancement. 
Had I been addressing a less scientific audience, I might have been tempted 
rather to boast of the achievements of engineers than to point out their shortcom- 
ings. The progress in many branches of mechanical science during the past fifty 
years has exceeded the anticipation of the most far-seeing. Fifty years ago the 
chairman of the Stockton and Darlington Railway, when asked by a Parliamentary 
committee if he thought any further improvements would be possible on railways, 
replied that he understood in future all new railways would have a high earth- 
work bank on each side to prevent engines toppling over the embankments and to 
-arrest hot ashes, which continually set fire to neighbouring stacks, but in other re- 
spects he appeared to think perfection was attained. Shortly before the introduc- 
‘tion of locomotives it was also thought perfection was attained when low trucks 
were attached to the trains to carry the horses over the portions of the line where 
descending grades prevailed, and all the newspapers announced, with a great 
flourish of trumpets, that a year’s experience showed the saving in horseflesh to be 
fully 35 per cent. 
Although these views seem childlike enough from our present standpoint, I 
‘have no doubt that as able and enterprising engineers existed prior to the age of 
‘steam and steel as exist now, and their work was as beneficial to mankind, though 
different in direction. In the important matter of water supply to towns, indeed, 
I doubt whether, having reference to facility of execution, even greater works were 
not done 2,000 years ago than now. Herodotus speaks of a tunnel 8 ft. square, 
and nearly a mile long, driven through a mountain in order to supply the city of 
Samos with water; and his statement, though long doubted, was verified in 1882 
‘through the abbot of a neighbouring cloister accidentally unearthing some stone 
slabs. The German Archeological Society sent out Ernst Fabricius to make a 
complete survey of the work and the record reads like that of a modern engineer- 
ing undertaking. Thus, from a covered reservoir in the hills proceeded an arched 
conduit about 1,000 yards long, partly driven as a tunnel and partly executed on 
the ‘cut and cover’ system adopted on the London underground railway. The 
tunnel proper, more than 1,100 yards in length, was hewn by hammer and ¢hisel 
‘through the solid limestone rock. It was driven from the two ends like the great 
Alpine tunnels, without intermediate shafts, and the engineers of 2,400 years ago 
might well be congratulated for getting only some dozen feet out of level and little 
more out of line. From the lower end of the tunnel branches were constructed to 
supply the city mains and fountains, and the explorers found ventilating shafts and 
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