office. The result is, that we see all over the country a great
number of highway bridges which have been sold by dishonest builders
to ignorant officials, and which are on the eve of falling, and await
only an extra large crowd of people, a company of soldiers, a
procession, or something of the sort, to break down.

Not many years ago, a new highway bridge of iron was to be made over
one of the principal rivers in New England. The county commissioners
desired a well-known engineer, especially noted as a bridge-builder,
to superintend the work, in order to see that it was properly
executed. The engineer, after inspection of the plans, told the
commissioners plainly that the design was defective, and would not
make a safe bridge; and that, unless it was materially changed, he
would have nothing to do with it. The bridge, however, was a cheap
one, and, as such, commended itself to the commissioners, who
proceeded to have it erected according to the original plan; and
these same commissioners now point to that bridge, which has not yet
fallen, but which is liable to do so at any time, as a complete
vindication of their judgment, so called, as opposed to that of the
engineer who had spent his life in building bridges.

An impression exists in the minds of many persons, that it is purely
a matter of opinion whether a bridge is safe, or not. In very many
cases, however,--perhaps in most,--it is not at all a matter of
opinion, but a matter of fact and of arithmetic. The whole question
always comes to this: Is the material in this bridge of good quality?
Is there enough of it? Is it correctly disposed, and properly put
together? With given dimensions, and knowing the load to be carried,
it is a matter of the very simplest computation to fix the size of
each member. We know what one square inch of iron will hold, and we
know, also, the total number of pounds to be sustained; and it is no
matter of opinion, but one of simple division, how many times one
will go into the other.

But it may be asked, Can the precise load which is coming upon any
structure be exactly fixed? are not the circumstances under which
bridges are loaded very different? Bridges in different localities
are certainly subjected to very different loads, and under very
different conditions; but the proper loads to be provided for have
been fixed by the best authority for all cases within narrow enough
limits for all practical purposes. Few persons are aware o