one between English and American systems of bridge building. The decision was 
that the long spans woro awarded to an American firm, Messrs. CLAEKE, EE- 
EVES & CO. , of Plioenixville, Pa. , and the short spans to English bridge-builders, 
tlio Fairbairn Manufacturing Company, of Manchester. Of the thirty-six plans 
submitted, only three or four were rejected on account of not coming up to special 
strength. 
The bridges of Clavko, Ecoves & Co. were selected for the long spans, not only 
as being unclonbtedly first-class, both in material and workmanship, but also as be- 
ing the lowest responsible tender. Somo curiosity lias been expressed to know how 
American bridgo-builders, using liigh-priced iron, and paving higlicr wages for labor 
than their English competitors, could jet build a less costly bridge. 
While it is to some extent true that the specifications allowed of a lower quality 
find loss expensive iron for tlio 100 than for tlio 200 foot span, yet one of tlio prin- 
cipal reasons why an American firm was lowest on the long and an English firm on 
tho short spans is owing to the less weight of iron roquiretl by tlio American system 
of bridge, an^l this is more apparent the longer tlio span. 
Somo persons erroiiGously suppose that tlio raoro iron thcro is in a bridge the 
stronger it will be. But a little reflection will show that it is only tlio iron that is 
working, or, in other words, that is actually strained by thd load, that contributes to 
the strength of the structure. All the rest is cload weight, and merely weighs down 
the bridge. 111 very short spans this ia not disadvantageous, as it tends to diminish 
vibration, but in long spans where the weight of the bridge much exceeds that of the 
load passing over it, every pound of iron that does not contribute to the strength of 
the bridge is a positive injury. To illustrate tliis more clearly : if one bridge weighs 
125 tons and another 250, and both are strained by the rolling load 10,000 pounds 
per square inch, tlio lighter is the stronger of the two. But if the 125 ton bridge be 
strained 10,000 pounds per square inch, wliile the 250 ton bridge is strained only 
0000 pounds per square inch, then tno latter has really double the strength and 
double the lifo of the former ; for half the iron may corrode away, and thon the worldng 
area of tlio bar will bo oqual. It is noi clearly perceiving this fnot — that the streng- 
th of the bridge depends upon tlio working area of each part — tliat has led our English 
friends to make such heavy bridges. 
In several plans, if the strains per square inch are alike for similar loads they 
must all bo of tlio same strength, providing the connections aro equally perfect. - 
Some take more iron than others to effect the result, but the result is the same. 
The lightness of American bridges is due — 1st, to tlio concentration of material 
along the lines of strain, which enabled a lighter web system to be used, and hence a 
higher truss ; 2d, to this greater lieiglit of truss, wlncli throws less leverage on tlio 
upper and lower chord system, and lienee requires loss iron in tlieir members ； 3d, to 
the use of eye and pin connections instead of rivets, by which there is no waste of 
metal to compensate for tlio doduotion of rivet- liolos. 
American bridges are stiffer vertically and better braced laterally than English 
bridges, tlieir greater hoiglit giving less deflection under a load, ancl allowing of 
overhead bracing as well as that below the track. 
