320 tons. If
we take off one engine, and fill its place with cars, we take off 60
tons, and put in its place 33 tons; i.e., we remove 27 tons, or just
about 1/12 of the working-load. Taking off a large part of the
working-load, however, is taking off a very small part of the
breaking-load; with a factor of safety of six, for example, taking
off 1/12 of the working-load is taking off less than 1/70 of the
breaking-load. An order, therefore, like that above, can only be of
use when the working-load and the breaking-load are so nearly alike
that the actual load is a dangerous one: that is when the bridge is
unfit for any traffic whatever; so that, if such an order was really
needed, it would, in itself, be, in the eyes of an engineer, a
condemnation of the bridge.

Having seen something of the structures which require inspecting, let
us now see what kind of inspection we have in this country, and the
result of it; and let us also see the inspection which we might have,
and the results that might be produced. Looking first at railroad
bridges, it might be supposed that no one could be so much interested
in keeping such structures in good order as the companies which own
those bridges, and which have the bills to pay in case of disaster.
This is, of course, so; but, in spite of the fact, the Ashtabula
bridge broke down, on one of the best managed lines in the country,
and cost the company over half a million dollars in damages. No
railroad bridge ever broke down, which the owners were not interested
in keeping safe; but there is always a desire to put off incurring
large expenses until the last moment, and thus weak bridges are very
often let go too long. A short time since, the superintendent of a
large railroad stated plainly before a legislative committee, that
many of the smaller roads were not safe to run over, but that such
roads were having a hard time, and could not afford to keep their
track and bridges in a safe condition. During the past ten years over
two hundred railroad bridges in the United States have broken down.
These bridges were all kept under such inspection as the railroad
companies owning them considered sufficient, or such as they could
afford; but either the supervision was defective, or the companies
knowingly continued the use of unsafe bridges, and this fault has by
no means been confined to the smaller and poorer roads. It would
seem, therefore, that inspection by the companies themselves has n