More than this, it has
repeatedly happened that a heavy train has passed over a bridge in
apparent safety, while a much lighter one passing directly afterwards
has gone through. In almost all such cases, the structure has been
weak and defective; and finally some heavy load passes over, and
cripples the bridge, so that the next load produces a disaster. For
the test of a bridge to be in any way satisfactory, we must know just
what effect such test has had upon the structure. We do not find this
out by simply standing near, and noting that the bridge did not
break down. We must satisfy ourselves beyond all question that no
part has been overstrained.

A short time ago the builders of a wretchedly cheap and unsafe
highway bridge, in order to quiet a fear which had arisen that the
structure was not altogether sound, tested a span 122 feet long with
a load of 58,000 pounds; and inasmuch as the bridge did not break
down under this load, which was less than a quarter part of what it
was warranted to carry safely, the county commissioners considered
the result eminently satisfactory, and remarked that the test was
made merely to satisfy the public that the bridge was abundantly safe
for all practical uses. The public would, no doubt, have been
satisfied that the Ashtabula bridge was abundantly safe for all
practical uses had it stood on that bridge in the morning and seen a
heavy freight-train go over it, and yet that very bridge broke down
directly afterwards under a passenger-train.

Now, according to the common notion, that was a good bridge in the
morning, and a very bad bridge, or rather, no bridge at all, in the
evening. The question for the public is, When did it cease to be a
good bridge, and begin to be a bad one? A test like the one referred
to above can do no more than illustrate the ignorance or lack of
honesty of those who make it, or those who are satisfied with it.
Such a test might come within a dozen pounds of breaking the bridge
down, and no one be the wiser. The entire absurdity of such testing
has recently been illustrated in the most decided manner. The very
same company that built the bridge above referred to, made also
another one on exactly the same plan, and of almost precisely the
same size, and tested it when done by placing almost exactly the same
load upon it. The bridge did not break down; and the county
commissioners, for whom the work was done, were satisfied that it was
"abundantly safe for