he Ashtabula bridge, it is stated in the report of the committee of
the Ohio Legislature appointed to investigate that disaster, had
factors,--we can hardly call them factors of safety,--in some parts
as low as 1-6/10 and 1-2/10, such factors referring to the
breaking-weight; and even these factors were obtained by assuming the
load as at rest, and making no allowance for the jar and shock from a
railroad train in motion. Well may the commissioners say, as they do
at the end of their report, "The bridge was liable to go down at any
time during the last ten years under the loads that might at any time
be brought upon it in the ordinary course of the company's business,
and it is most remarkable that it did not sooner occur."

One point always brought forward when an iron bridge breaks down, is
the supposed deterioration of iron under repeated straining; and we
are gravely told that after a while all iron loses its fibre, and
becomes crystalline. This is one of the "mysteries" which some
persons conjure up at tolerably regular intervals to cover their
ignorance. It is perfectly well known by engineers the world over,
that with good iron properly used, nothing of the kind ever takes
place. This matter used to be a favorite bone of contention among
engineers, but it has long since been laid upon the shelf. No
engineer at the present day ever thinks of it. We have only to allow
the proper margin for safety, as our first-class builders all do, and
this antiquated objection at once vanishes. The examples of the long
duration of iron in large bridges are numerous and conclusive. The
Niagara-Falls railroad suspension bridge was carefully inspected
after twenty-five years of continued use under frequent and heavy
trains, and not only was it impossible to detect by the severest
tests any defect in the wire of the cables, but a piece of it, being
thrown upon the floor, curled up, showing the old "kink" which the
iron had when it was first made, and wound on the reel. The Menai
suspension bridge, in which 1,000 tons of iron have hung suspended
across an opening of 600 feet for sixty years, shows no depreciation
that the most rigid inspection could detect. Iron rods, recently
taken from an old bridge in this country, have been carefully tested
after sixty years of use, and found to have lost nothing, either of
the original breaking-strength, or of the original elasticity.

The question is frequently asked, Does not extreme cold weak