The towers, however, were designed to sustain a heavy train and
locomotive and to withstand the terrific wind of the monsoon. The
pressure of such a wind on a 320-foot tower is tremendous. The bridge
was completed within the specified time and bore without flinching all
the severe tests to which it was put. Heavy trains--much heavier than
would ordinarily be run over the viaduct--steamed slowly across the
great steel trestle while the railroad engineers examined with utmost
care every section that would be likely to show weakness. But the
designers had planned well, the steel-workers had done their full duty,
and the American bridgemen had seen to it that every rivet was properly
headed and every bolt screwed tight--and no fault could be found.

The bridge engineer's work is very diversified, since no two bridges are
alike. At one time he might be ordered to span a stream in the midst of
a populous country where every aid is at hand, and his next commission
might be the building of a difficult bridge in a foreign wilderness far
beyond the edge of civilisation.

Bridge-building is really divided into four parts, and each part
requires a different kind of knowledge and experience.

First, the designer has to have the imagination to see the bridge as it
will be when it is completed, and then he must be able to lay it out on
paper section by section, estimating the size of the parts necessary for
the stress they will have to bear, the weight of the load they will have
to carry, the effect of the wind, the contraction and expansion of cold
and heat, and vibration; all these things must be thought of and
considered in planning every part and determining the size of each. Also
he must know what kind of material to use that is best fitted to stand