never will know whether the iron is good or bad, nor whether the dimensions and proportions are such as to be safe or not. You will know that you have paid your money away, but you never will know what you have got for it until some day when your bridge gets a crowd upon it, and breaks down, and you have the damage to pay. This mode of buying a bridge is very common. To buy a good bridge, first determine precisely what you want; and if you don't know any thing in regard to bridge-building yourself, employ an engineer who does, to make a specification stating exactly what you want, and what you mean to have. Then advertise for bridge-builders to send in plans and proposals. Let the contractors understand that all plans and computations are to be submitted to your engineer, that all materials and workmanship will be submitted to your inspectors, and that the whole structure is to be made subject to the supervision of a competent engineer, and accepted by him for you. You will find at once, that, under such conditions, all travelling agents and builders of cheap bridges will avoid you as a thief does the light of day. You will have genuine proposals from responsible companies, and their bids should be submitted to your engineer. When you have made your choice, let the contract be written by your lawyer, and have the plans and specifications attached. Employ a competent engineer to inspect the work as it goes on; and when it is done, you will have a bridge which will be warranted absolutely sound by the best authority. This mode of buying a bridge is very uncommon. The 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."