“The bridges built in the last five or six years are perfectly safe, unless two trains 
should meet or a train run off the edge. Both of these accidents are extremely im- 
probable. The railroad companies allow no iron bridges, improperly constructed, to 
remain. There are, to be suit — or so I have hoard — a good many unsafe bridges, 
probably hundreds of them. Ifc will take timo for these to be replaced by iron or 
steel ones. The great danger with wooden bridges is from cinders and sparks. Theso 
drop on the wood, cliar in a little, and weaken tho s true bur o until an unusually 
heavy train or sudden jar causes ft crash. Tlicro liavo been lmiulreds of accidents 
from this cause. So the wooden bridges must go. An iron bridge costs little more. 
We’ve always been ahead of the world in bridge building, and wo intend to stay 
there. M 
Tho following extract from the 14 Delaware Bridge Company’s Album ’’ boars 
upon wliat I have already said concerning bridge designing in America being a 
specialty. 
“ The construction of wrought iron bridges has attained such development 
"witliin tho past 10 years as to be now recognized as a separate and important braucli 
of constructive engineering, essentially depending for its succoss upon tho skill, ex- 
perience ami integrity of the engineer, who lias specially devoted bimseU* to the study 
find practice of tbo subject. 
Good iron bridges are occasionally built by engineers in general practice, and 
thero aro still a few railroad companies which li.avo a bridge construction depavt- 
mon ^ I but as a rule, bridges are builfc to-day by men who have onileavorccl to acquaint 
themselves with the intricate questions involved in the application of tlio general 
theory of skeleton structures to practice, and who have found that tbo subject was 
capable of a sufficient development to absorb their exclusive attention. In other 
words, bridges are built to-day by bridge-builders, ami to become a britlge-builtler 
demands such an amount of technical knowledge, coupled with, and partly the result 
of， largo experience in design, and in tlio manipulation of materials, as will ensure 
tlio erection of structures which are not only scientifically sound in principle, but at 
the samo time economical and durable. M 
The following from an article in tlio Chicago Railroad Gazette of J uly 1870 wp- 
“ English and American Iron Bridges n will also couiinn sonic of my state uiouts. 
“ Some two months ago tenders were solicited for tho construction of iron rail- 
w«iy bridges of spans of 100 and 200 feet, by the Intercolonial Railway of Canada, 
connecting Quebec and Halifax. This call was very generally rosponded to, tlicn.o 
being tenders put in by nine fee en English, ono Belgian, aiul sixfcoeu Americ.an Lritlgc- 
builders. 
Tlie specification, wliicli was a rigid ono, called for uniformity of strength， hut 
the design open to each person. The bridges wero all to be of wrought iron, 
capablo of bearing 1 \ gross tons per lineal foot, in additiou to their own weight, 
straining the iron in tension to over 10,000 poumls per square inch, riio 
】 rou of* the 200 fee fc spans was to be capable of bearing 00,000 poiuuls per square 
iuch before breaking, and that of the 100 feet spans 50,000 pouiula per square incli. 
Much interest was felt as to the result of this competition, which was viftaally 
